Homeotropic alignment liquid crystal film, optical film comprising the same, and image display device

ABSTRACT

A homeotropic alignment liquid crystal film is provided with a liquid crystalline substance containing a side chain liquid crystalline compound having an oxetanyl group, as a constituent, aligned homeotropically on an alignment substrate while being in a liquid crystal state and fixed in the homeotropic alignment by allowing the oxetanyl group to react. Thus, the homeotropic alignment liquid crystal film can be stably produced without necessitating a complicated step such as light irradiation under an inert gas atmosphere and is excellent in alignment retainability after being fixed in the homeotropic alignment and in mechanical strength.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/781,460, filed Jul. 23, 2007, issued as U.S. Pat. No. 7,732,024,which is a continuation of International Application No.PCT/JP2006/301607, filed Jan. 25, 2006, which was published in theJapanese language on Aug. 17, 2006, under International Publication No.2006/085454, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to homeotropic alignment liquid crystalfilms. The homeotropic alignment liquid crystal films of the presentinvention alone or in combination with other optical films may be usedas optical films such as retardation films, viewing angle compensators,elliptical polarizers, and brightness enhancement films. The presentinvention also relates to image display devices comprising suchhomeotropic alignment liquid crystal films, such as liquid crystaldisplay devices, organic EL display devices, and PDPs.

Optical films with a refractive index anisotropy have taken industriallyimportant roles as used for enhancing the image quality of a liquidcrystal display device. The optical films with a refractive indexanisotropy may be broadly classified into those produced by stretchingplastic films and those produced by aligning liquid crystallinesubstances. The latter are more worthy of attention because they havepotentials that they achieve structures with various refractive indices.

Films having a larger refractive index in the thickness direction areassumed to be effective in improving the viewing angle of a liquidcrystal display device. It is assumed that the use of a homeotropicalignment (vertically aligned) liquid crystal is a close approach toobtain such films. The homeotropic alignment of liquid crystal moleculesdenotes that the longitudinal axes of liquid crystal molecules arealigned substantially vertically relative to the substrate. It is wellknown that the homeotropic alignment can be obtained by applyingelectric field to a pair of glass substrates sandwiching a liquidcrystal as done in a liquid crystal display device. However, it is verydifficult to form the aligned liquid crystal into a film, and theprocesses having been reported so far have possessed many problems.

For example, in the processes disclosed in the following PatentDocuments 1 to 3, the film is obtained by allowing a main chainpolymeric liquid crystalline compound to be homeotropically aligned andfixing the compound by vitrification. It is assumed that in thehomeotropic alignment, the molecules of the polymeric compound arealigned in the thickness direction and thus there is a concern thatcracking is likely to occur in the plane direction. However, in theseprocesses, no technical measure of for example strengthening thematerials by cross linking is taken. In the process disclosed in PatentDocument 4, the homeotropic alignment of a side chain polymeric liquidcrystalline compound is fixed by vitrification. However, there is aconcern in terms of strength that is more serious than where a mainchain polymeric liquid crystalline compound is used. In the processesdisclosed in Patent Documents 5 and 6 below, a polymerizable lowmolecular weight liquid crystalline compound is added to a side chainpolymeric liquid crystalline compound, but there is a limit inreinforcement thereof because the low molecular weight liquidcrystalline compound is solely polymerized.

In the process disclosed in Patent Document 7 below, a material is usedwherein a radically polymerizable group or a cationically polymerizablegroup such as vinyl ether and epoxy groups is introduced into a sidechain polymeric liquid crystalline compound. However, in general,radical polymerization undergoes oxygen inhibition and may proceedinsufficiently, leading the necessity of large facilities or apparatusfor removal of oxygen. The vinyl ether or epoxy group is advantageous inthis regard because it does not encounter oxygen inhibition. However,there is a concern that the ether bond of the vinyl ether group isunstable and tends to cleave. It is difficult to introduce the epoxygroup into a liquid crystalline material and obtain a highpolymerization degree when cross linking is carried out. Furthermore,since a large amount of non-liquid crystalline structural units isintroduced into the liquid crystalline material in order to obtain thehomeotropic alignment, there still remains a concern regarding thestable exhibition of liquid crystallinity. As described above, therehave been remains problems in the conventional production of ahomeotropic alignment liquid crystal film.

An image display device such as a liquid crystal display device variesin contrast associated with a change in viewing angle due to thebirefringence of the liquid crystal or the like. For the purpose ofpreventing such contrast variations, a technique has been proposedwherein a retardation film is arranged on the liquid crystal cell of aliquid crystal device so as to compensate the optical characteristicsrelating to birefringence thereby improving the viewing anglecharacteristics. A uniaxial or biaxial stretched film is used as such aretardation film for compensation. However, such a stretched film doesnot necessarily have viewing angle characteristics satisfactory to allliquid crystal cells.

Patent Document 8 discloses a continuously carried-out process forproducing a retardation film, characterized in that on one or bothsurfaces of an elongate thermoplastic resin film is bonded one or moreheat-contractive films, and the elongate film is held with the grips ofa tenter and contracted in the width direction at Magnification A whichis in the range of 0.7 or more to less than 1.0, by allowing thecontraction force of the heat-contraction films to be acted, followed bystretching and widening the elongate film at a stretch ratio (%) meetingthe requirement that the percentage is equal to or less than thatrepresented by (100-Magnification A×100)×0.15 where the film widthexcluding the parts held by the grips after the contraction is 100.

In this process, the film is also stretched in the thickness direction,resulting in a retardation film having a retardation in the thicknessdirection. However, when the main refractive indices in the resultingretardation film plane and the refractive index in the retardation filmthickness direction are nx and ny, and nz, respectively and nx>ny, Nzdefined by Nz=(nx−nz)/(nx−ny) will be −1.0<Nz<0.1. Therefore, there is alimit in stretching in the thickness direction, and thus the retardationin the thickness direction can not be controlled in a wide range.Furthermore, since in this process, the elongate film is stretched inthe thickness direction by heat contraction, the resulting retardationfilm will be thicker than the elongate film. That is, the retardationfilm produced by this process has a thickness of 50 to 100 μm, which isnot thin enough to meet the low profiling required in a liquid crystaldisplay device or the like.

In the process disclosed in Patent Document 9, a retardation film isproduced which a homeotropic alignment liquid crystal film and astretched film with a retardation function are integrally laminated. Theprocess for producing the homeotropic alignment liquid crystal film isthe same as that disclosed in Patent Document 7 and is insufficientbecause the conventional processes including this process still haveproblems.

In the vertical alignment mode, which is one of the display modes of aliquid crystal display device, the liquid crystal molecules are alignedvertically to the substrate when no electric voltage is applied theretoand produces a black image when linear polarizers are arranged in acrossing relation to each other on both sides of the liquid crystalcell.

The optical characteristics in the liquid crystal cell is isotropic inthe plane direction, and thus an ideal viewing angle compensationtherefor can be easily achieved. When an optical element with a negativeuniaxial optical anisotropy in the thickness direction of the liquidcrystal cell is inserted between one or both surfaces thereof and thelinear polarizers in order to compensate the positive uniaxial opticalanisotropy in the liquid crystal cell thickness direction, veryexcellent black image viewing angle characteristics can be obtained.

Upon application of an electric voltage, the liquid crystal moleculeschanges their alignment from the vertical direction relative to thesubstrate surface toward the parallel direction. Thereupon, it isdifficult to make the liquid crystal alignment uniform. The use of ausual alignment treatment, i.e., a rubbing treatment on the substrateresults in a significant deterioration in display quality.

There are proposals for making the liquid crystal alignment uniform uponapplication of an electric voltage that a uniform alignment is obtainedby modifying the shape of the electrodes on the substrates so that anoblique electric field is generated in the liquid crystal layer.Although this method enables the liquid crystal alignment to be uniform,an uneven alignment region is produced when viewed at the micro leveland will be a dark region upon application of an electric voltage.Therefore, the transmissivity of the liquid crystal display device willbe diminished.

Patent Document 11 proposes a configuration wherein the linearpolarizers arranged on the both surfaces of a liquid crystal cell havinga liquid crystal layer which may be in a random alignment are replacedby circular polarizers. Replacement of the linear polarizers by circularpolarizers each of which is a combination of a linear polarizer and a ¼wavelength plate can eliminate the dark region produced upon applicationof an electric voltage and accomplish to produce a liquid crystaldisplay device with high transmissivity. However, the vertical alignmenttype liquid crystal display device with the circular polarizers has aproblem that it has narrower viewing angle characteristics than thatwith the linear polarizers.

Patent Document 12 proposes an optical anisotropic element with anegative uniaxial optical anisotropy or a biaxial optical anisotropicmaterial for compensating the viewing angle of a vertical alignment typeliquid crystal display device with circular polarizers. However,although the optical anisotropic element with a negative uniaxialoptical anisotropy can compensate the positive uniaxial opticalanisotropy in the cell thickness direction, it fails to compensate theviewing angle characteristics of the ¼ wavelength plate, resulting ininsufficient viewing angle characteristics.

Patent Document 1: Japanese Patent Publication No. 2853064

Patent Document 2: Japanese Patent Publication No. 3018120

Patent Document 3: Japanese Patent Publication No. 3078948

Patent Document 4: Japanese Patent Laid-Open Publication No. 2002-174725

Patent Document 5: Japanese Patent Laid-Open Publication No. 2002-333524

Patent Document 6: Japanese Patent Laid-Open Publication No. 2002-333642

Patent Document 7: Japanese Patent Laid-Open Publication No. 2003-2927

Patent Document 8: Japanese Patent Laid-Open Publication No. 2002-304924

Patent Document 9: Japanese Patent Laid-Open Publication No. 2003-149441

Patent Document 10: Japanese Patent Laid-Open Publication No. 2003-2927

Patent Document 11: Japanese Patent Laid-Open Publication No. 2002-40428

Patent Document 12: Japanese Patent Laid-Open Publication No.2003-207782

BRIEF SUMMARY OF THE INVENTION

The present invention provides a homeotropic alignment liquid crystalfilm which can be produced stably without the necessity of complicatedsteps such as photo-irradiation under an inert gas atmosphere and isexcellent in alignment retainability after being fixed in a homeotropicalignment and in mechanical strength; a laminated retardation film whichcan control the retardation in the thickness direction in a wide range;and a viewing angle compensator with excellent viewing anglecharacteristics as well as image display devices such as liquid crystaldisplay devices, comprising an optical film such as a brightnessenhancement film comprising the homeotropic alignment liquid crystalfilm.

The present invention was accomplished as the results of extensivestudies carried out to solve the above-described problems.

That is, the present invention relates to a homeotropic liquid crystalfilm comprising a liquid crystalline substance containing a side chainliquid crystalline compound having an oxetanyl group, as a constituent,aligned homeotropically on an alignment substrate while the substance isin a liquid crystal state and fixed in the homeotropic alignment byallowing the oxetanyl group to react.

Alternatively, the present invention also relates to a homeotropicliquid crystal film comprising a liquid crystalline substance containinga side chain liquid crystalline compound having an oxetanyl group, as aconstituent, aligned homeotropically on an alignment substrate while thesubstance is in a liquid crystal state and fixed in the homeotropicalignment by allowing the oxetanyl group to react, and satisfying thefollowing requirements:

[1] 0 nm≦Re≦200 nm

[2] −500 nm≦Rth≦−30 nm

wherein Re indicates the retardation value in the liquid crystal filmplane, Rth indicates the retardation value in the liquid crystal filmthickness direction, and Re and Rth are defined by Re=(Nx−Ny)×d andRth=(Nx−Nz)×d, respectively, wherein d is the liquid crystal filmthickness [nm], Nx and Ny are the main refractive indices in the liquidcrystal film plane, Nz is the main refractive index in the thicknessdirection, and Nz>Nx≧Ny.

The present invention also relates to an optical film comprising thehomeotropic liquid crystal film and to an image display devicecomprising the optical film.

Furthermore, the present invention also relates to a laminatedretardation film comprising a liquid crystal layer comprising a liquidcrystalline substance containing a side chain liquid crystallinecompound having an oxetanyl group, as a constituent, alignedhomeotropically on an alignment substrate while the substance is in aliquid crystal state and fixed in the homeotropic alignment by allowingthe oxetanyl group to react, and a stretched film with a retardationfunction integrally laminated with on the liquid crystal layer, and aprocess for producing such a laminated retardation film.

The present invention also relates to a viewing angle compensator for avertical alignment type liquid crystal display device, comprising aliquid crystal film comprising a liquid crystalline substance containinga side chain liquid crystalline compound having an oxetanyl group, as aconstituent, aligned homeotropically on an alignment substrate while thesubstance is in a liquid crystal state and fixed in the homeotropicalignment by allowing the oxetanyl group to react.

The present invention also relates to a vertical alignment type liquidcrystal display device comprising the viewing angle compensatortherefor.

The present invention will be described in more detail below.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a conceptual view for illustrating the liquid crystal displaydevices used in Examples 2, 5 and 6;

FIG. 2 is a conceptual view for illustrating the liquid crystal displaydevices used in Examples 4 and 7;

FIG. 3 is a schematic cross-sectional view of the vertical alignmenttype liquid crystal display of Example 8;

FIG. 4 is a plan view indicating the angular relations of each of thecomponents of the vertical alignment type liquid crystal display ofExample 8;

FIG. 5 is a view indicating the contrast ratio when viewing the verticalalignment type liquid crystal display of Example 8 from all thedirections;

FIG. 6 is a schematic cross-sectional view of the vertical alignmenttype liquid crystal display of Example 9;

FIG. 7 is a plan view indicating the angular relations of each of thecomponents of the vertical alignment type liquid crystal display ofExample 9;

FIG. 8 is a view indicating the contrast ratio when viewing the verticalalignment type liquid crystal display of Example 9 from all thedirections;

FIG. 9 is a schematic cross-sectional view of the transflective verticalalignment type liquid crystal display of Example 10;

FIG. 10 is a plan view indicating the angular relations of each of thecomponents of the transflective vertical alignment type liquid crystaldisplay of Example 10;

FIG. 11 is a view indicating the contrast ratio when viewing thetransflective vertical alignment type liquid crystal display of Example10 from all the directions;

FIG. 12 is a schematic cross-sectional view of the vertical alignmenttype liquid crystal display of Comparative Example 2;

FIG. 13 is a plan view indicating the angular relations of each of thecomponents of the vertical alignment type liquid crystal display ofComparative Example 2;

FIG. 14 is a view indicating the contrast ratio when viewing thevertical alignment type liquid crystal display of Comparative Example 2from all the directions;

FIG. 15 is a schematic cross-sectional view of the transflectivevertical alignment type liquid crystal display of Comparative Example 3;

FIG. 16 is a plan view indicating the angular relations of each of thecomponents of the transflective vertical alignment type liquid crystaldisplay of Comparative Example 3; and

FIG. 17 is a view indicating the contrast ratio when viewing thetransflective vertical alignment type liquid crystal display ofComparative Example 3 from all the directions.

DETAILED DESCRIPTION OF THE INVENTION

Selections of liquid crystal materials and alignment substrates areextremely important upon production of the liquid crystal film fixed ina homeotropic alignment according to the present invention.

First of all, the liquid crystal materials will be described.

Liquid crystal materials which may be used in the present invention arethose (liquid crystalline substances) containing at least a side chainliquid crystalline polymeric compound having an oxetanyl group, as aconstituent. Specific examples of such materials include thosecontaining mainly a side chain liquid crystalline polymer such aspoly(meth)acrylates and polysiloxanes, having at one of its terminalends a polymerizable oxetanyl group. More specifically, preferredexamples include side chain liquid crystalline polymeric compoundsproduced by homopolymerizing or copolymerizing the (meth)acrylic portionof a (meth)acrylic compound having an oxetanyl group represented byformula (1) below with another (meth)acrylic compound:

wherein R₁ is hydrogen or methyl, R₂ is hydrogen, methyl, or ethyl, L₁and L₂ are each a single bond, —O—, —O—CO— or —CO—O—, M is representedby any of formulas (2) to (4) below, and m and n are each an integer of0 to 10:—P₁-L₃-P₂-L₄-P₃—  (2)—P₁-L₃-P₃—  (3)—P₃—  (4)wherein P₁ and P₂ are each a group represented by formula (5) below, P₃is a group represented by formula (6) below, and L3 and L4 are each asingle bond, —CH═CH—, —C≡C—, —O—, —O—CO—, or —CO—O—:

There is no particular restriction on the method of synthesizing the(meth)acrylic compound having an oxetanyl group represented by formula(1). Therefore, there may be used any conventional method utilized inthe field of organic chemistry. For example, a portion having anoxetanyl group is coupled to a portion having a (meth)acrylic group bymeans of the Williamson's ether synthesis or an ester synthesis using acondensing agent thereby synthesizing a (meth)acrylic compound havingtwo reactive functional groups, i.e., an oxetanyl group and a(meth)acrylic group.

A side chain polymeric liquid crystalline compound containing a unitrepresented by formula (7) below is produced by homopolymerizing the(meth)acrylic group of a (meth)acrylic compound having an oxetanyl grouprepresented by formula (1) or copolymerizing the same with another(meth)acrylic compound:

There is no particular restriction on the polymerization conditionswhich, therefore, may be those for ordinary radical or anionpolymerization.

As an example of the radical polymerization, a method may be used inwhich a (meth)acrylic compound is dissolved in a solvent such asdimethylformamide (DMF) and reacted at a temperature of 60 to 120° C.for several hours using 2,2′-azobisisobutylonitrile (AIBN) or benzoylperoxide (BPO) as an initiator. Alternatively, in order to allow theliquid crystal phase to be stably exhibited there is an effective methodin which living radical polymerization is conducted using an initiatorsuch as a copper (II) bromide/2,2′-bipyridyl-based initiator or a2,2,6,6-tetramethylpiperidinyloxy free radical (TEMPO)-based initiatorso as to control the molecular weight distribution. These radicalpolymerizations are needed to be conducted strictly under deoxidationconditions.

As an example of the anionic polymerization, a method may be used inwhich a (meth)acrylic compound is dissolved in a solvent such astetrahydrofuran (THF) and reacted using a strong base such as organiclithium compounds, organic sodium compounds or the Grignard reagent asan initiator. Alternatively, this polymerization can be converted toliving anionic polymerization by optimizing the initiator or reactiontemperature thereby controlling the molecular weight distribution. Theseanionic polymerizations are needed to be conducted strictly underdehydration and deoxidation conditions.

There is no particular restriction on types of a (meth)acrylic compoundadded to be copolymerized as long as the resulting polymeric substanceexhibits liquid crystallinity. However, preferred are (meth)acryliccompounds having a mesogen group because they can enhance the liquidcrystallinity of the resulting polymeric substance. More specifically,particularly preferred are those as represented by the followingformulas:

In the above formulas, R is hydrogen, an alkyl group having 1 to 12carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or a cyanogroup.

The side chain liquid crystalline polymeric compound used as the liquidcrystal material in the present invention contains a unit of formula (7)in an amount of preferably 5 to 100 percent by mole, particularlypreferably 10 to 100 percent by mole. The side chain liquid crystallinepolymeric compound has a weight average molecular weight of preferably2,000 to 100,000, particularly preferably 5,000 to 50,000.

Other than the above-described side chain liquid crystalline polymericcompounds, the liquid crystal material used in the present invention maycontain various compounds which may be mixed therewith out impairing theliquid crystallinity. Examples of such compounds include those having acationic polymerizable functional group such as oxetanyl, epoxy, andvinylether groups; various polymeric compounds having a film formingcapability; and various low molecular- or polymeric-liquid crystallinecompounds exhibiting liquid crystallinity. When the side chain liquidcrystalline polymeric compound is used in the form of a composition, thepercentage of the compound in the whole composition is preferably 10percent by mass or more, preferably 30 percent by mass or more, morepreferably 50 percent by mass or more. When the side chain liquidcrystalline polymeric compound is contained in an amount of less than 10percent by mass, the concentration of the polymerizable group in thecomposition will be low, resulting in insufficient mechanical strengthafter polymerization.

In the present invention, the liquid crystal material is homeotropicallyaligned and fixed in the homeotropic alignment by polymerizingcationically the oxetanyl group to be cross-linked.

Therefore, the liquid crystal material preferably contains a photo- orthermal-cation generator which generates cations with an externalstimulus such as light or heat. If necessary, various sensitizers may beused in combination.

The term “photo cation generator” used herein denotes a compound whichcan generate cations by irradiating a light with a specific wavelengthand may be any of organic sulfonium salt-, iodonium salt-, orphosphonium salt-based compounds. Counter ions of these compounds arepreferably antimonate, phosphate, and borate. Specific examples includeAr₃S⁺SbF₆ ⁻, Ar₃P⁺BF₄ ⁻, and Ar₂I⁺PF₆ ⁻ wherein Ar indicates a phenyl orsubstituted phenyl group. Sulfonic acid esters, triazines,diazomethanes, β-ketosulfones, iminosulfonates, and benzoinsulfonatesmay also be used.

The term “thermal cation generator” used herein denotes a compound whichcan generate cations by being heated to a certain temperature and may beany of benzylsulfonium salts, benzylammonium salts, benzylpyridiniumsalts, benzylphosphonium salts, hydrazinium salts, carbonic acid esters,sulfonic acid esters, amineimides, antimony pentachloride-acetylchloride complexes, diaryliodonium salt-dibenzyloxy coppers, andhalogenated boron-tertiary amine adducts.

Since the amount of the cation generator to be added in thepolymerizable liquid crystalline composition varies depending on thestructures of the mesogen portion or spacer portions constituting theside chain liquid crystalline polymer to be used, the equivalent weightof the oxetanyl group, and the conditions for aligning the compositionin a liquid crystal state, it can not be determined with certainty.However, it is within the range of usually 100 ppm by mass to 20 percentby mass, preferably 1,000 ppm by mass to 10 percent by mass, morepreferably 0.2 percent by mass to 7 percent by mass, and most preferably0.5 percent by mass to 5 percent by mass. An amount of the cationgenerator of less than 100 ppm by mass is not preferable becausepolymerization may not progress due to the insufficient amount of cationto be generated. An amount of the cation generator of more than 20percent by mass is not also preferable because a large amount of theundecomposed residue of the cation generator remains in the resultingliquid crystal film and thus the light resistance thereof would bedegraded.

The alignment substrate will be described next.

The alignment substrate which may be used in the present invention ispreferably a substrate with a flat and smooth surface. Examples of sucha substrate include films or sheet formed of organic polymericmaterials, glass sheets, and metals. It is preferred to use materialssuch as organic polymeric materials, in view of cost and continuousproductivity. Examples of the organic polymeric materials includepolyvinyl alcohols, polyimides, polyphenylene sulfides, polyphenyleneoxides, polyetherketones, polyetheretherketones, polyether sulfones,polyethylene naphthalates, polyethylene terephthalates, polyarylates,and triacetyl cellulose. The organic polymeric materials may be usedalone as an alignment substrate or in the form of film formed on anothersubstrate.

In order to obtain the homeotropic alignment stably using theabove-described liquid crystal material, the material forming analignment substrate preferably has a long chain (usually 4 or more,preferably 8 or more carbon atoms and there is no particular restrictionon the upper limit, but usually 50 or fewer, preferably 40 or fewer)hydrocarbon group (in particular, alkyl or alkenyl group). Amongst, mostpreferred are polyvinyl alcohols (PVA) having a long chain hydrocarbon.

Examples of the long chain hydrocarbon include alkyl groups such asbutyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, andeicosane groups, oleyl, and eicosenyl groups.

There is no particular restriction on PVA. However, in view ofpolymerization degree, preferred are those with a polymerization degreeof 100 or greater and 3000 or less, and more preferred are those with apolymerization degree of 200 or greater and 2000 or less. In view ofsaponification degree, preferred are those with a saponification degreeof 60% or higher, and more preferred are those with a saponificationdegree of 80% or higher. A PVA with a polymerization degree of less than100 would be insufficient in strength as an alignment film while a PVAwith a polymerization degree of greater than 3000 would make itdifficult to prepare a solution for coating and to use the solution. APVA with a saponification degree of less than 60% would be insufficientin heat resistance as an alignment film and fail to perform its functionsufficiently because the alignment film would be corroded with asolution of the liquid crystal material when the solution is coated onthe alignment film.

In the field of the liquid crystal, a substrate is generally rubbed withcloth for aligning a liquid crystal material, so-called rubbingtreatment. However, the homeotropic alignment of the present inventionis an alignment structure wherein anisotropy in the film plane does notsubstantially occurs and thus does not always need a rubbing treatment.However, with the objective of suppressing the liquid crystal from beingrepelled when it is coated on an alignment film, a weak rubbingtreatment is preferably carried out. An important set value forregulating the rubbing conditions is the peripheral velocity ratio. Theperipheral velocity ratio denotes a ratio of the moving velocity of therubbing cloth to the moving velocity of the substrate when a rubbingcloth wrapped around a roll is rolled and rubs over a substrate. Theweak rubbing treatment denotes a rubbing treatment carried out byrotating the rubbing cloth at a peripheral velocity ratio of usually 1.5or greater and 50 or less, preferably 2 or greater and 25 or less, andparticularly preferably 3 or greater and 10 or less. A peripheralvelocity ratio of less than 1.5 would cause deficient peeling orreleasing when a peel off step described below is carried out. Aperipheral velocity ratio of greater than 50 would be too strong rubbingeffect which fails to align the liquid crystal material in a completevertical position, which material is tilted toward the plane directionrather than the vertical direction. A so-called fixed rubbing treatmentwherein only the substrate is conveyed over the rubbing roll which isnot rotated but is fixed may be used as a weak rubbing treatment.

The method of producing the liquid crystal film of the present inventionwill be described next.

Although not restricted, the liquid crystal film may be produced byspreading the above-described liquid crystal material over theabove-described alignment substrate so as to be aligned and fixed in analigned state by photo-irradiation or heat treatment.

The method of forming a liquid crystal material layer by spreading theliquid crystal material over the alignment substrate may be a methodwherein the liquid crystal material in a molten state is directly coatedover the alignment substrate or a method wherein a solution of theliquid crystal material is coated over the alignment substrate and driedto evaporate the solvent.

There is no particular restriction on the solvent used for preparing thesolution as long as it can dissolve the liquid crystal material and beevaporated under appropriate conditions. Preferred examples of thesolvent include ketones such as acetone, methyl ethyl ketone,isophorone, and cyclohexanone; ether alcohols such as butoxy ethylalcohol, hexyloxy ethyl alcohol, and methoxy-2-propanol; glycol etherssuch as ethylene glycol dimethylether and diethylene glycol dimethylether; esters such as ethyl acetate and ethyl lactate; phenols such asphenol and chlorophenol; amides such as N,N-dimethylformamide,N,N-dimethylacetoamide, and N-methylpyrrolidone; halogens such aschloroform, tetrachloroethane, and dichlorobenzene; and mixturesthereof. Surfactants, defoaming agents, or leveling agents may be addedto the solution so as to form a uniform film layer on an alignmentsubstrate.

Regardless of whether the liquid crystal material is coated directly orin the form of a solution, there is no particular restriction on themethod of coating the liquid crystal material as long as the uniformityof the film layer can be maintained. For example, there may be used spincoating, die coating, curtain coating, dip coating, and roll coatingmethods.

The coating of a solution of the liquid crystal material is preferablyfollowed by a drying step for removal of the solvent after coating.There is no particular restriction on the drying step as long as it canmaintain the uniformity of the coated film, which may be anyconventional method. For example, there may be used a method using aheater (furnace) or a hot air blowing.

The liquid crystal material layer formed on the alignment substrate ishomeotropically aligned by a heat treatment or the like and then curedby photo-irradiation and/or a heat treatment so as to be fixed in thehomeotropic alignment. The first heat treatment (carried out for formingthe liquid crystal) aligns the liquid crystal material homeotropicallyby heating the material at a temperature in such a range that the liquidcrystal material exhibits a liquid crystal phase, synergistically withthe action of the above-described alignment substrate.

Since the conditions for the heat treatment vary in optimum conditionsand limits depending on the liquid crystal phase behavior temperature(transition temperature) of the liquid crystal material to be used, itcan not be determined with certainty. However, the heat treatment isconducted at a temperature within the range of usually 10 to 250° C.,preferably 30 to 160° C., more preferably at a temperature higher thanthe Tg of the liquid crystal material, more preferably at a temperaturehigher by 10° C. or higher than the Tg of the liquid crystal material. Atoo low temperature is not preferable because there is a possibilitythat the liquid crystal material may not be aligned sufficiently, whilea too high temperature is not also preferable because the alignabilityof an alignment film substrate may be adversely affected. The heattreatment is conducted for usually 3 seconds to 30 minutes andpreferably 10 seconds to 10 minutes. A heat treatment for shorter than 3seconds is not preferable because there is a possibility that the liquidcrystal material may not be aligned in a liquid crystal phasecompletely. Whereas, a heat treatment for longer than 30 minutes is notalso preferable because the productivity is diminished.

As described above, after the liquid crystal material is alignedhomeotropically by a heating treatment, it is cured (cross-linked) bypolymerizing the oxetanyl group therein while being retained in thehomeotropic aligned state. The liquid crystal material is fixed in thehomeotropic aligned state by the curing (cross-linking) reaction andthen modified into a stronger film.

As described above, since the liquid crystal material used in thepresent invention has a polymerizable oxetanyl group, it is preferred touse a cationic polymerization initiator (cation generator) forpolymerizing (cross-linking) the reactive group. As such a cationgenerator, a photo-cation generator is preferred to a thermal-cationgenerator.

In the case of using a photo-cation generator, after addition thereof,the processes up to the heating treatment for aligning the liquidcrystal material are conducted under such dark conditions (conditionswhere light is shielded to an extent that the photo-cation generatordoes not dissociate) that the liquid crystal material does not cureuntil subjected to the aligning process and thus can be alignedhomeotropically while maintaining sufficient flowability. Thereafter, alight from a light source capable of emitting an appropriate wavelengthof light is irradiated so as to allow the photo-cation generator togenerate cations thereby curing the liquid crystal material whilemaintaining the homeotropic alignment.

The light irradiation is conducted by irradiating a light from a lightsource having a spectrum in an absorption wavelength region of thephoto-cation generator to be used, such as a metal halide lamp, ahigh-pressure mercury lamp, a low-pressure mercury lamp, a xenon lamp,an arc discharge lamp, and a laser thereby decomposing the photo-cationgenerator. The irradiation dose per cm² is within the range of generally1 to 2,000 mJ and preferably 10 to 1,000 mJ in the integratedirradiation dose. However, when the absorption region of thephoto-cation generator is extremely different from the spectrum of thelight source, or the liquid crystal material itself can absorb a lightin the wavelength of the light source, the irradiation dose is notlimited to the above range. In these cases, a method may be employed inwhich a suitable photo sensitizer or two or more types of photo-cationgenerators having different absorption wavelengths may be used.

The temperature upon light irradiation needs to be within such a rangethat the liquid crystal material is aligned in a liquid crystal phase.Furthermore, the light irradiation is preferably conducted at atemperature which is equal to or higher than the Tg of the liquidcrystal material, in order to enhance the efficiency of the curingsufficiently.

The liquid crystal layer produced through the above-described processesbecomes a sufficiently solid and strong film. More specifically, sincethe three-dimensional bond of the mesogen portion is achieved by thecuring reaction, the liquid crystal layer is significantly improved notonly in heat-resistance (the upper limit temperature at which the liquidcrystal phase is maintained) but also in mechanical strength such asresistance to scratch, wear, and cracking compared with that beforebeing cured.

In the case where there arise problems that the alignment substrate tobe used is not optically isotropic, the resulting liquid crystal film isopaque at a wavelength region where it is intended to be used, or thealignment substrate is so thick that it causes a problem in practicaluse, the liquid crystal layer may be transferred to an opticallyisotropic substrate film or a substrate film which is transparent at awavelength region where the liquid crystal film is intended to be usedor to a substrate film temporarily until the liquid crystal film isattached to a liquid crystal cell.

The transferring method may be any conventional method. For example, asdisclosed in Japanese Patent Laid-Open Publication Nos. 4-57017 and5-333313, a method may be used in which after a substrate film differentfrom the alignment substrate, for transferring is laminated via a tackyadhesive or adhesive over a liquid crystal layer on the alignmentsubstrate and if necessary a tacky adhesive or adhesive is coated overthe other surface, on which the liquid crystal film layer is notlaminated, of the substrate film for transferring and then cured, onlythe liquid crystal film is transferred on the substrate film fortransferring by releasing the alignment substrate. Examples of thetransparent substrate onto which the liquid crystal layer is transferredinclude triacetyl cellulose films such as Fujitac (manufactured by FujiPhoto Film Co., Ltd.) and Konicatac (manufactured by Konica Corp.); TPXfilm (manufactured by Mitsui Chemical Inc.); transparent films such asAfton film (manufactured by JSR), Zeonex film (manufactured by ZeonCorp.), and Acryplene film (manufactured by Mitsubishi Rayon Co., Ltd.);and a polyethylene terephthalate film treated with silicone or providedon its surface with a releasable layer. If necessary, the liquid crystalfilm may be directly transferred to a polarizing film.

There is no particular restriction on the tacky adhesive or adhesive tobe used for transferring the liquid crystal film as long as it is ofoptical grade. Therefore, there may be used conventional acrylic-,epoxy-, or urethane-based adhesives.

When the thickness is d [nm], the main refractive indices in the filmplane are Nx and Ny, the main refractive index in the film thicknessdirection is Nz, and Nx≧Ny in the homeotropic alignment liquid crystalfilm, preferably the retardation value in the film plane (Re=(Nx−Ny)×d)is from 0 to 200 nm, and the retardation value in the film thicknessdirection (Rth=(Nx−Nz)×d) is from −500 to −30 nm.

The Re and Rth values which are optical parameters of the homeotropicalignment liquid crystal film can not be determined with certaintybecause they depend on whether the liquid crystal film is used as abrightness enhancement film or a viewing angle improvement film for aliquid crystal display device or depend on the mode thereof or variousoptical parameters when the liquid crystal film is used as a viewingangle improvement film. However, the retardation value in thehomeotropic alignment film plane (Re) is adjusted within the range ofusually from 0 nm to 200 nm, preferably from 0 nm to 100 nm, morepreferably from 0 nm to 50 nm with respect to a monochromic light of 550nm while the retardation value in the thickness direction (Rth) isadjusted within the range of usually from −500 nm to −30 nm, preferablyfrom −400 nm to −50 nm, more preferably from −400 nm to −100 nm withrespect to a monochromic light of 550 nm.

Adjustment of the Re and Rth values within the above ranges makes itpossible that when the liquid crystal film is used an viewing angleimprovement film for a liquid crystal display device, the viewing anglethereof can be widened, compensating the color tone and that when theliquid crystal film is used as a brightness enhancement film, anexcellent brightness enhancement effect can be expected. An Re value oflarger than 200 nm would degrade the front characteristics of the liquidcrystal display device due to the affect of the large front retardationvalue. An Rth of larger than −30 nm or smaller than −500 nm would failto obtain sufficient viewing angle improving effect or cause unnecessarycoloration when the liquid crystal display device is viewed obliquely.

The thickness of the liquid crystal film can not be determined withcertainty because it depends on the mode of a liquid crystal displaydevice or various optical parameters but is usually from 0.2 μm to 10μm, preferably from 0.3 μm to 5 μm, more preferably from 0.5 μm to 2 μm.A film thickness of less than 0.2 μm would fail to obtain sufficientviewing angle improving effect or brightness enhancing effect. A filmthickness of greater than 10 μm cause unnecessary coloration on theliquid crystal display device.

The homeotropic alignment liquid crystal film produced as describedabove can be quantified by measuring the optical retardation at an anglewherein the liquid crystal film is tilted from a vertical incidence. Theoptical retardation value of the homeotropic alignment liquid crystalfilm is in contrast with respect to the vertical incidence. There may beused various methods for the optical retardation measurement. Forexample, an automated birefringence measuring device (manufactured byOji Scientific Instruments) and a polarization microscope may be used.The homeotropic alignment liquid crystal film looks black betweencrossed nicols polarizers. In this manner, the homeotropic alignabilitywas evaluated.

The homeotropic alignment liquid crystal film of the present inventionmay be laminated with one or more other optical films so as to form anoptical film.

For example, the homeotropic alignment liquid crystal film may bearranged between a cholesteric liquid crystal film and a ¼ wavelengthplate so as to form a brightness enhancement film. The cholestericliquid crystal film and ¼ wavelength plate may be any of thoseconventionally used in a brightness enhancement film without anylimitation.

Examples of the cholesteric liquid crystal film include those exhibitingcharacteristics that they reflect either one of right-handed orleft-handed circularly polarized light and transmit the other, such asaligned films of cholesteric liquid crystalline polymers and such filmssupported on a film substrate. The cholesteric liquid crystal film maybe any of those exhibiting circular dichroism in a part of spectrum ofvisible light or exhibiting circular dichroism in a spectrum of 200 nmor more in a visible light. The cholesteric liquid crystal film may beformed from a cholesteric liquid crystal polymer containing an opticallyactive group-containing monomer as a monomer unit. Since the pitch ofthe cholesteric liquid crystal varies on the basis of the content of theoptically active group-containing monomer, the circular dichroism can becontrolled with the content of the monomer unit. The thickness of thecholesteric liquid crystal film is preferably usually from 1 to 30 μm,particularly preferably from 2 to 15 μm. The cholesteric liquid crystalfilm may be blended with one or more additives such as a polymer otherthan the above-described polymers or a stabilizer, an inorganic compoundsuch as plasticizer, an organic compound, metal, a compound thereof ifnecessary.

The cholesteric liquid crystal film may be of an overlaid structure oftwo or more layers with different reflection wavelength in combinationso that it can reflect a circularly polarized light in a wide wavelengthrange such as a visible light region thereby producing a transmissivecircularly polarized light in a wide wavelength range.

In a brightness enhancement film which is a type of transmitting acircularly polarized light, such as the cholesteric liquid crystal film,it may allow the circularly polarized light to be made incident directlyto a polarizer. However, preferably the circularly polarized light isconverted to a linearly polarized light through a retardation film andthen is made incident to the polarizer with the objective of suppressingthe absorption loss. The use of a ¼ wavelength plate as the retardationfilm can convert a circularly polarized light to a linearly polarizedlight.

The ¼ wavelength plate may be any of those selected depending on thepurposes of use. Optical characteristics such as retardation can becontrolled by laminating two or more ¼ wavelength plates. Examples ofthe retardation film include birefringence films obtained by stretchingfilms formed from appropriate polymers such as polycarbonates,norbornene resins, polyvinyl alcohols, polystyrenes, polymethylmethacrylates, polypropylenes, other polyolefins, polyarylates, andpolyamides; aligned films formed from liquid crystal materials such asliquid crystal polymers; and aligned layers of liquid crystal materialssupported on a film. The thickness of the ¼ wavelength plate ispreferably from 0.5 to 200 μm, particularly preferably from 1 to 100 μm.

The retardation film functioning as a ¼ wavelength plate in a widewavelength region such as a visible light region may be obtained by amethod wherein for example, a retardation layer functioning as a ¼wavelength plate with respect to a pale color light of a wavelength of550 nm is overlaid on a retardation layer exhibiting other retardationcharacteristics, such as a retardation layer functioning as a ½wavelength plate. Therefore, the retardation film arranged between thepolarizer and the brightness enhancement film may be composed of one ormore retardation layers.

The brightness enhancement film may be produced by forming thehomeotropic alignment liquid crystal film on the ¼ wavelength plate usedas a substrate and laminating the cholesteric liquid crystal film via atacky adhesive layer on the homeotropic alignment liquid crystal film.Alternatively, the brightness enhancement film may be produced bytransferring the homeotropic alignment liquid crystal film formed on asubstrate to either one of the cholesteric liquid crystal film or the ¼wavelength plate via a tacky adhesive layer and laminating the otherthereon via a tacky adhesive layer.

There is no particular restriction on the tacky adhesive forming thetacky adhesive layer. There may be used any tacky adhesive appropriatelyselected from those containing a polymer such as an acrylic polymer, asilicone-based polymer, a polyester, a polyurethane, a polyamide, apolyether, a fluorine- or rubber-based polymer as a base polymer. Inparticular, it is preferred to use a tacky adhesive such as an acrylictacky adhesive which is excellent in optical transparency and in weatherresistance and heat resistance and exhibits tackiness characteristicssuch as moderate wetness, cohesivity and adhesivity.

The formation of the tacky adhesive layer may be carried out by anysuitable method. As an example, there is a method wherein a base polymeror a composition thereof is dissolved or dispersed in a solventcontaining toluene or ethyl acetate alone or in combination therebypreparing a tacky adhesive solution containing 10 to 40 percent by massof the adhesive, which solution is then directly laid over theabove-described substrate or liquid crystal film by an appropriatedeveloping method such as casting or coating or alternatively wherein atacky adhesive layer is formed in accordance with the method asdescribed above on a separator and then transferred onto the liquidcrystal layer. The tacky adhesive layer may contain additives such asnatural or synthetic resins, in particular fillers or pigmentscontaining tackiness-imparting resins, glass fibers, glass beads, metalpowders, and other inorganic powders, dyes, anti-oxidants. The tackyadhesive layer may contain fine particles so as to exhibit lightdiffusivity.

When the homeotropic alignment liquid crystal film formed on a substrateis transferred via a tacky adhesive layer, the homeotropic alignmentliquid crystal film may be subjected to a surface treatment. There is noparticular restriction on the method of the surface treatment. There maybe suitably used a surface treatment such as corona discharge,sputtering, low-pressure UV irradiation, or plasma treatment, which canmaintain the transparency of the liquid crystal film surface. Amongthese surface treatments, corona discharge treatment is excellent.

A polarizing film is used as an optical film applied to an image displaydevice such as a liquid crystal display device. The homeotropicalignment liquid crystal film or brightness enhancement film of thepresent invention is used in the form of a laminate with an optical filmsuch as a polarizing film.

A polarizing film wherein a polarizing film and the brightnessenhancement film are laminated is arranged on the rear side of theliquid crystal cell for actual use. The brightness enhancement filmexhibits characteristics that it reflects a linearly polarized lightwith a certain polarization axis or a circularly polarized light in acertain direction, upon incidence of light from the backlight of theliquid crystal display device or natural light reflected at the rearside of the liquid crystal cell and transmits the other light. Thepolarizing film wherein a polarizing film and the brightness enhancementfilm are laminated produces a transmitted light in a certainpolarization state by making an incident of light from the light sourcesuch as a backlight and does not transmit but reflects the light otherthan the light in the certain polarization state. The light reflected onthe brightness enhancement film surface is reversed by a reflectionlayer arranged on the rear side of the enhancement film so as to be madeincident thereto again, and the whole or a part of the incident light isallowed to transmit in the form of the light in the certain polarizedstate thereby increasing the amount of the light transmitting throughthe brightness enhancement film and enhancing the brightness byincreasing the amount of the light by supplying the polarized lightwhich is hard to be absorbed by the polarizer, to be used for liquidcrystal image display.

That is, when a light is made incident from the rear side of the liquidcrystal cell with the backlight, through the polarizer, without usingthe brightness enhancement film, most of the light having thepolarization direction which does not correspond to the polarizationaxis of the polarizer is absorbed thereby and does not transmit throughthe polarizer. That is, about 50 percent of the light is absorbed by thepolarizer though depending on the characteristics of the polarizer, andthus the amount of the light which can be used for liquid crystal imagedisplaying is decreased by the amount, resulting in dark images. Thebrightness enhancement film repeatedly reflects the light in thepolarization direction which can be absorbed by the polarizer, notallowing the light to be made incident thereto and further reverses thelight by a reflection layer arranged on its rear side so as to be madeincident to the brightness enhancement film again. The brightnessenhancement film transmits and supplies only the polarized lightreflected and reversed between the film and the reflection film, thepolarization direction of which polarized light is changed so as to beallowed to transmit through the polarizer. As the result, the brightnessenhancement film can use the light from the backlight efficiently forthe image display of a liquid crystal display device and thus canbrighten the viewing surface thereof.

The polarizing film has usually a protective film on one or both surfaceof a polarizer. There is no particular restriction on the polarizer.There may be used various polarizers. Examples of the polarizer includethose obtained by stretching uniaxially a hydrophilic polymer film suchas a polyvinyl alcohol-based film, a partially formalized polyvinylalcohol-based film or an ethylene-vinyl acetate copolymer-basedpartially saponified film to which a dichroic substance such as iodineor a dichroic dye is allowed to absorb; and polyene-based alignmentfilms such as dehydrated products of PVA and dehydrochlorinated productsof polyvinyl chloride. Among these polarizers, it is suitable to usethose obtained by stretching and aligning a polyvinyl alcohol-based filmto which a dichroic substance (iodine or dye) is allowed to absorb.There is no particular restriction on the thickness of the polarizer.There is no particular restriction on the thickness of the polarizer. Itis, however, general to use a polarizer with a thickness of 5 to 80 μm.

The polarizer wherein a polyvinyl alcohol is dyed with iodine anduniaxially stretched may be produced by dipping a polyvinyl alcohol inan aqueous solution of iodine to be dyed and stretching it 3 to 7 timeslonger than the original length. If necessary, the polyvinylalcohol-based film may be dipped in a solution of boric acid orpotassium iodide. Further if necessary, the polyvinyl alcohol-based filmmay be dipped in water to be washed before dyeing. Washing of thepolyvinyl alcohol-based film can remove stains thereon and a blockinginhibitor and swells the film thereby providing an effect to preventuneven dyeing. Stretching may be carried out after or while dyeing withiodine or followed by dyeing with iodine. Alternatively, stretching maybe carried out in an aqueous solution of boric acid or iodine or a waterbath.

The protection film to be arranged on one or both surfaces of thepolarizer are preferably excellent in transparency, mechanical strength,thermal stability, moisture shielding capability, and isotropy. Examplesof materials of the protection film include polyester-based polymerssuch as polyethylene terephthalate and polyethylene naphthalate;cellulose-based polymers such as diacetyl cellulose and triacetylcellulose; acryl-based polymers such as polymethyl methacrylate;styrene-based polymers such as polystyrene and acrylonitrile styrenecopolymers (AS resin); and polycarbonate-based polymers. Anotherexamples include polyolefin-based polymers such as polyethylene-,polypropylene- and cycloolefin-based polyolefins, polyolefins having anorbornene structure, and ethylene propylene copolymers; vinylchloride-based polymers; amide-based polymers such as nylon and aromaticpolyamides; imide-based polymers; sulfone-based polymers; polyethersulfone-based polymers; polyetheretherketone-based polymers;polyphenylene sulfide-based polymers; vinyl alcohol-based polymers;vinylidene chloride-based polymers; vinyl butyral-based polymers;acrylate-based polymers; polyoxymethylene-based polymers; epoxy-basedpolymers; and blends of these polymers. Another examples include thoseobtained by forming acryl-, urethane-, acrylurethane-, epoxy-, andsilicone-based thermal or ultraviolet curing type resins, into film. Thethickness of the protection film is generally 500 μm or less, preferablyfrom 1 to 300 μm, particularly preferably from 5 to 200 μm.

The protection film is preferably a cellulose-based polymer such astriacetyl cellulose in view of polarization characteristics anddurability. Particularly preferred is a triacetyl cellulose film. Whenthe protection film is arranged on both surface of the polarizer, theprotection film on the top surface may be formed with the same ordifferent polymer of the protection film on the bottom surface. Thepolarizer is attached to the protection film via a water-based tackyadhesive. Examples of the water-based tacky adhesive include polyvinylalcohol-based adhesives, gelatin-based adhesives, vinyl-based latex,water-based polyurethanes, and water-based polyesters.

The protection film may be subjected to hard coat or anti-reflectiontreatment or various treatments for the purposes of anti-sticking,diffusion, or anti-glare.

The hard coat treatment is carried out for preventing scratching on thepolarizing film surfaces by forming a curable film with excellenthardness or slipping characteristics, with a suitable acryl- orsilicone-based ultraviolet curing resin, on the protection film surface.The anti-reflection treatment is carried out for preventing externallight from reflecting on a polarizing film surface and may be achievedby forming an anti-reflection film in accordance with a conventionalmanner. The anti-sticking treatment is carried out for preventingadhesion between the adjacent layers.

The anti-glare treatment is carried out for preventing the inhibition ofvisibility of a light transmitting through the polarizing film caused bythe reflection of the natural light on a polarizing film surface, byforming fine irregularities on a protection film surface by roughingsuch as sand blasting or embossing or by blending transparent fineparticles. Examples of the fine particles to be blended for forming thefine irregularity on the protection film surface include transparentfine particles, for example, inorganic fine particles of an averageparticle diameter of 0.5 to 50 μm, which may be electrically conductive,such as silica, alumina, titania, zirconia, tin oxide, indium oxide,cadmium oxide, and antimony oxide and organic fine particles such ascross-linked or uncross-linked polymers. When the fine irregularity isformed on the protection film surface, the amount of the fine particlesis usually from 2 to 50 parts by weight, preferably from 5 to 25 partsby weight, on the basis of 100 parts by weight of the transparent resinforming the fine surface irregularity. The anti-glare layer may also bea diffusion layer (having a function of enlarging the viewing angle) forenlarging the light transmitting through the polarizing film and thusenlarging the viewing angle.

The anti-reflection layer, anti-sticking layer, diffusion layer andanti-glare layer may be formed integrally on the protection film or maybe formed as an additional optical layer separately from the transparentprotection layer.

The above-described polarizing film may be used as an elliptical orcircular polarizing film in the form of a laminate with a retardationfilm. The elliptical or circular polarizing film is now described. Thispolarizing film changes a linearly polarized light to an elliptically orcircularly polarized light, an elliptically or circularly polarizedlight to a linearly polarized light, or the polarization directionthereof, due to the presence of the retardation film. In particular, asa retardation film for changing a linearly polarized light to acircularly polarized light or a circularly polarized light to a linearlypolarized light, a ¼ wavelength plate is used. A ½ wavelength plate isusually used for changing the polarization direction of a linearlypolarized light.

The elliptical polarizing film is effectively used so as to compensate(prevent) coloration (blue or yellow) caused by the birefringence of theliquid crystal layer of a super twisted nematic (STN) type liquidcrystal display device thereby allowing the device to display the blackand white image with no such coloration. Preferably, the ellipticalpolarizing film can control a three dimensional birefringence becausecoloration occurring when viewing the screen of a liquid crystal displaydevice can be compensated (prevented). The circular polarizing film iseffectively used so as to adjust the color tone of the image of areflection type liquid crystal display device whose image is colored andalso has an anti-reflection function.

The retardation film may be any of plates of various wavelengths orthose for compensating coloration caused by the birefringence of aliquid crystal layer or the viewing angle. A laminate of two or moreretardation films with appropriate retardations selected depending onthe purpose of use can control optical characteristics such asretardation. As the retardation film, there may be used theabove-exemplified retardation films and the homeotropic alignment liquidcrystal film of the present invention alone or in combination with otherfilms.

The retardation film may be used as a viewing angle compensatorlaminated with the polarizing film to provide a wide viewing anglepolarizing film. The viewing angle compensator is a film for wideningthe viewing angle of the screen of a liquid crystal display device so asto allow the image to appear relatively clear even when the screen isviewed slightly from an oblique direction not vertically.

As the viewing angle compensating retardation film, there may also beused a film stretched uniaxially or biaxially or stretched in twodirections crossing each other and a two-way stretched film such as atilt alignment film. Examples of the tilt alignment film include thoseobtained by stretching and/or contracting a polymer film bonded to aheat contractive film under the contraction force thereof by heating andthose obtained by subjecting a liquid crystal polymer film to tiltalignment. The viewing angle compensator may be used in any suitablecombination for the purposes of preventing coloration due to changes inviewing angle caused by the retardation of the liquid crystal cell andenlarging the viewing angle of excellent visibility.

Alternatively, with the objective of achieving the wide viewing angle ofexcellent visibility, the retardation film is preferably an opticallycompensating retardation film comprising an optically anisotropic layersuch as an aligned liquid crystal polymer layer, in particular a tiltalignment layer formed from a discotic liquid crystal polymer or a barlike liquid crystal polymer, supported on a triacetyl cellulose film.

There is no particular restriction on an optical film laminated foractual use other than those described above. For example, there may beused one or more optical layers such as a reflection plate and atransflective plate, which have been conventionally used for a liquidcrystal display device. In particular, examples of such optical layersinclude reflection or transflection type polarizing films obtained bylaminating a reflection or transflection plate on the elliptical orcircular polarizer.

The reflection type polarizing film comprises the polarizing film and areflection layer arranged thereon and is used in a liquid crystaldisplay device which displays images by reflecting an incident lightfrom the viewing side (displaying side) and thus has an advantage thatit can be thinned because no light source such as a backlight is notnecessarily built-in. The reflection type polarizing film may be formedby any suitable method wherein a reflection layer of metal is overlaidon one surface of the polarizing film if necessary via a transparentprotection layer.

Specific examples of the reflection type polarizing film include thoseobtained by overlaying a foil or vacuum deposited film of a reflectivemetal such as aluminum on one surface of a protection film, whichsurface may be subjected to a matt treatment if necessary. Anotherexamples include those having a reflection layer with fine irregularityformed on a protection film with fine irregularity obtained by blendingfine particles thereto. The reflection layer with fine irregularity hasadvantages that it can prevent directivity or dazzling appearance andsuppress unevenness in contrast by reflect diffusely an incident light.The fine particle-containing protection film has advantages thatunevenness in contrast can be suppressed more because an incident lightor reflected light thereof is diffused when it transmits through theprotection film. The reflection layer with fine irregularitycorresponding to that of the protection film may be formed by overlayingmetal on the surface of the protection film using a suitable method suchas vacuum deposition, ion-plating, or sputtering.

Instead of overlaying the reflection plate directly on the protectionfilm of the polarizing film, the reflection plate may be used in theform of a reflection sheet comprising a reflection layer and a suitablefilm like the transparent film forming the protection film. Since thereflection layer is usually formed of metal, it is preferably used, withits reflection surface covered with a protection film or the polarizingfilm with the objective of preventing the reflectivity from diminishingdue to oxidation, maintaining the initial reflectivity for a long periodof time, and avoiding the necessity of overlaying an additionalprotection layer.

The transflection type polarizing film may be obtained by forming on thepolarizing film a transflection type reflection layer such as ahalf-mirror, reflecting the above-mentioned light and transmitting theother light. The transflection type polarizing film is generallyarranged on the rear side of the liquid crystal cell of a liquid crystaldisplay device which displays images by reflecting an incident lightfrom the viewing side (displaying side) when the device is used underrelatively bright conditions and displays images with the aide of abuilt-in light source such as a backlight built-in the rear side of thetransflection type polarizing film when the device is used underrelatively dark conditions. That is, the transflection type polarizingfilm is effectively used for a liquid crystal display device which cansave energy required for the use of a light source such as a backlightunder bright conditions and can use a built-in light source underrelatively dark conditions.

The polarizing film may be a laminate of the polarizing film and two ormore optical layers, just like the above-describedpolarization-separative type polarizers. Therefore, the polarizing filmmay be a reflection or transflection type elliptical polarizing filmwhich is a combination of the above-described reflection ortransflection type polarizing film and a retardation film.

The elliptical polarizing film or reflection type elliptical polarizingfilm comprises the polarizing film or the reflection type polarizingfilm and a retardation film laminated in a suitable combination. Theelliptical polarizing film may be formed by laminating a (reflectiontype) polarizing film and a retardation film individually andsequentially so as to be a combination thereof during the process ofproducing a liquid crystal display device. However, it is advantageousto use an optical film produced by laminating the polarizing film andthe retardation film beforehand because the optical film is excellent inquality stability and lamination workability, leading to an improvementin the production efficiency of a liquid crystal display device or thelike.

On the optical film of the present invention may be formed a tackyadhesive layer. The tacky adhesive layer may be used for bonding theoptical film to a liquid crystal cell or for laminating optical layers.When the optical film is bonded, the optical axis may be oriented at anappropriate angle depending on the intended retardation characteristics.

There is no particular restriction on the tacky adhesive forming thelayer thereof. Examples of the tacky adhesive include those used forlaminating the homeotropic alignment liquid crystal film and thesubstrate for transferring. The tacky adhesive layer may be provided inthe same manner.

The tacky adhesive layer may be arranged in the form of an overlaidlayer of those with different compositions or types, on one or bothsurfaces of the polarizing film or optical film. When the tacky adhesivelayer is arranged on both surfaces, the tacky adhesive layer on the topsurface of the polarizing film or optical film may be the same as ordifferent from that on the bottom surface.

The thickness of the tacky adhesive layer may be determined depending onthe purpose of use or bond strength and is generally from 1 to 500 μm,preferably from 5 to 200 μm, particularly preferably from 10 to 100 μm.

The exposed surface of the tacky adhesive layer is temporarily coveredwith a separator before use for the purpose of preventing the layer frombeing contaminated. Whereby, any access to the tacky adhesive layer canbe prevented during the normal handling. The separator may be anysuitable separator which has been conventionally used, such as thoseobtained by coating a releasing agent such as silicone-, long-chainalkyl-, fluorine-based agent or molybdenum sulfide on a suitable foliatebody such as plastic films, rubber sheets, paper, cloth, unwoven fabric,net, foamed sheets, metal foils, and laminates thereof.

In the present invention, the polarizer, transparent protection film,optical film or tacky adhesive layer forming the above-describedpolarizing film may be treated with an ultraviolet absorber selectedfrom salicylic acid ester-based compounds, benzophenone-based compounds,benzotriazole-based compounds, cyanoacrylate-based compounds, and nickelcomplex salt-based compounds so as to have ultraviolet absorptivity.

The optical films of the present invention are preferably used forproducing various devices such as liquid crystal display devices.Particularly preferably, the optical films are used as viewing angleimprovement films for liquid crystal display devices.

The liquid crystal display device may be produced by any conventionalmethod. That is, the liquid crystal display device is generally producedby assembling components such as a liquid crystal cell, optical filmsand if necessary an illumination system and incorporating thereto adriving circuit. However, there is no particular restriction on themethod except for using the optical films of the present invention.Therefore, the liquid crystal display device may be produced inaccordance with any conventional method. There is no particularrestriction on the type of the liquid crystal devices to be produced,which may, therefore, be any of various liquid crystal display devicessuch as transmissive, reflective and transflective liquid crystaldevices.

Examples of such liquid crystal cell modes include TN (Twisted Nematic),STN (Super Twisted Nematic), VA (Vertical Alignment), MVA (multi-domainvertical alignment), OCB (Optically Compensated Bend), ECB (ElectricallyControlled Birefringence), HAN (Hybrid-Aligned Nematic), IPS (In-PlaneSwitching), Bistable Nematic, ASM (Axially Symmetric Aligned Microcell),Half Tone Gray Scale modes, and display modes using a ferroelectricliquid crystal and an antiferroelectric liquid crystal.

The liquid crystal alignment in the cell may have a singledirectionality in the cell plane and may be used in a liquid crystaldisplay device wherein the alignment is divided. Examples of the liquidcrystal display devices with regard to methods of applying an electricvoltage to the liquid crystal cell include those driven in a passivemode using ITO electrodes and an active mode using TFT (Thin FilmTransistor) electrodes and TFD (Thin Film Diode) electrodes.

A liquid crystal display device may be produced wherein a polarizingfilm and an optical film are individually arranged on one or bothsurfaces of the liquid crystal cell or wherein a backlight or areflection plate is used as an illumination system. Here, the opticalfilm of the present invention may be arranged on one or both sides ofthe liquid crystal cell. When the polarizing film and optical film arearranged on both sides of the liquid crystal cell, the polarizing filmand optical film on the upper side may be the same as or different fromthose arranged on the lower side. Furthermore, one or more suitablecomponents such as a diffusive plate, an anti-glare layer, ananti-reflection film, a protection plate, a prism array, a lens arraysheet, a light diffusing plate, and a backlight may be arranged atappropriate positions in a liquid crystal display device.

The present invention also provides a laminated retardation filmcomprising a liquid crystal layer comprising a liquid crystallinesubstance containing a side chain liquid crystalline compound having anoxetanyl group as a constituent, aligned homeotropically on an alignmentsubstrate while the substance is in a liquid crystal state and fixed inthe homeotropic alignment by allowing the oxetanyl group to react, and astretched film with a retardation function integrally laminated on theliquid crystal layer.

The liquid crystal layer comprising a liquid crystalline substancecontaining a side chain liquid crystalline compound having an oxetanylgroup as a constituent, aligned homeotropically on an alignmentsubstrate while the substance is in a liquid crystal state and fixed inthe homeotropic alignment by allowing the oxetanyl group to react can bequantified by measuring the retardation of the liquid crystal layer atan angle tilted from the vertical incident.

When the main refraction indices in the plane are Nx1 and Ny1, therefraction index in the thickness direction is Nz1 and the thickness d1(μm)=on the order of 1 to 10 in the resulting homeotropic alignmentliquid crystal layer, (Nx1−Ny1)=on the order of 0 to 0.0005, and(Nx1−Nz1)=on the order of −0.1800 to −0.2000 for liquid crystal layersproduced using the materials in Examples described below. In general,Nx1=on the order of 1.53 to 1.55, Ny1=on the order of 1.53 to 1.55, andNz1=on the order of 1.72 to 1.74.

When Nz1>Nx1≧Ny1 in the homeotropic alignment liquid crystal layer usedin the laminated retardation film, the retardation value in the plane(Re1=(Nx1−Ny1)×d1 [nm]) is preferably from 0 to 50 nm, and theretardation value in the thickness direction (Rth1=(Nx1−Nz1)×d1 [nm]) ispreferably from −500 to −30 nm.

The Re1 and Rth1 values which are optical parameters of the homeotropicalignment liquid crystal layer can not be determined with certaintybecause they depend on the usage such as whether the layer is used as abrightness enhancement film or a viewing angle improvement film for aliquid crystal display device and further depend on the display mode ofthe liquid crystal display device and various optical parameters whenthe layer is used as a viewing angle improvement film. However, withrespect to a monochromic light of 550 nm, the retardation value (Re1) inthe homeotropic alignment liquid crystal layer plane is adjusted tousually from 0 nm to 50 nm, preferably from 0 nm to 20 nm, morepreferably from 0 nm to 5 nm and the retardation value (Rth1) in thethickness direction is adjusted to usually from −500 to −30 nm,preferably −400 to −50 nm, more preferably from −400 to −100 nm.

Adjustment of the Re1 and Rth1 values within the above ranges results ina viewing angle improvement film for a liquid crystal display devicewhich can widen the viewing angle while compensating the color tone ofthe images and results in a brightness enhancement film which canprovide excellent brightness enhancement effect. When the Re1 value islarger than 50 nm, the front characteristics of the liquid crystaldisplay device would be degraded due to the large front retardationvalue. When the Rth1 value is larger than −30 nm or smaller than −500nm, sufficient viewing angle improving effect may not be attained orunnecessary coloration may occur when viewing the device obliquely.

Next, the stretched film having a retardation function will bedescribed.

Examples of the stretched film include birefringence films obtained bystretching a suitable polymer such as polycarbonates, norbornene resins,polyvinyl alcohols, polystyrenes, polymethyl methacrylates,polypropylenes, and other polyolefins, polyarylates, and polyamides;aligned films formed from liquid crystal materials such as liquidcrystal polymers; and aligned layers of a liquid crystal materialsupported on a film.

When the main refraction indices in the plane are Nx2 and Ny2, therefraction index in the thickness direction is Nz2, Nx2>Ny2 and thethickness d2 (μm)=on the order of 25 to 30 in the stretched film,(Nx2−Ny2)=on the order of 0.0040 to 0.0060, and (Nx2−Nz2)=on the orderof 0.0040 to 0.0060 for stretched films produced using the materials inExamples described below. In general, Nx2=on the order of 1.593 to1.5942, Ny2=on the order of 1.5850 to 1.5887, and Nz2=on the order of1.5850 to 1.5833.

When Nx2>Ny2 in the stretched film having a retardation function film,the retardation value in the plane (Re2=(Nx2−Ny2)×d2 [nm]) is preferablyfrom 30 to 500 nm, and the retardation value in the thickness direction(Rth2=(Nx2−Nz2)×d2 [nm]) is preferably from 30 to 300 nm.

The Re2 and Rth2 values which are optical parameters of the stretchedfilm having a retardation function can not be determined with certaintybecause they depend on the usage such as whether the layer is used as abrightness enhancement film or a viewing angle improvement film for aliquid crystal display device and further depend on the display mode ofthe liquid crystal display device and various optical parameters whenthe layer is used as a viewing angle improvement film. However, withrespect to a monochromic light of 550 nm, the retardation value (Re2) inthe stretched film plane is adjusted to usually from 30 nm to 500 nm,preferably from 50 nm to 400 nm, more preferably from 100 nm to 300 nmand the retardation value (Rth2) in the thickness direction is adjustedto usually from 30 to 300 nm, preferably 50 to 200 nm, more preferablyfrom 70 to 150 nm.

Adjustment of the Re2 and Rth2 values within the above ranges results ina viewing angle improvement film for a liquid crystal display devicewhich can widen the viewing angle while compensating the color tone ofthe images and results in a brightness enhancement film which canprovide excellent brightness enhancement effect. When the Re2 value issmaller than 30 nm or larger than 500 nm, sufficient viewing angleimproving effect may not be attained or unnecessary coloration may occurwhen viewing the device obliquely. When the Rth2 value is smaller than30 nm and larger than 300 nm, sufficient viewing angle improving effectmay not be attained or unnecessary coloration may occur when viewing thedevice obliquely.

The laminated retardation film of the present invention may be producedby forming the homeotropic alignment liquid crystal layer on thestretched film having a homeotropic alignability and retardationfunction, as a substrate. Alternatively, the laminated retardation filmmay be produced by transferring the homeotropic alignment liquid crystallayer formed on an alignment substrate having a homeotropic alignabilityto the stretched film having a retardation function via a tacky adhesivelayer.

There is no particular restriction on the tacky adhesive forming thetacky adhesive layer. There may be used any tacky adhesive appropriatelyselected from those containing a polymer such as an acrylic polymer, asilicone-based polymer, a polyester, a polyurethane, a polyamide, apolyether, a fluorine- or rubber-based polymer as a base polymer. Inparticular, it is preferred to use a tacky adhesive such as an acrylictacky adhesive which is excellent in optical transparency and in weatherresistance and heat resistance and exhibits tackiness characteristicssuch as moderate wetness, cohesivity and adhesivity.

The formation of the tacky adhesive layer may be carried out by anysuitable method. As an example, there is a method wherein a base polymeror a composition thereof is dissolved or dispersed in a solventcontaining toluene or ethyl acetate alone or in combination therebyobtaining a tacky adhesive solution containing 10 to 40 percent by massof the adhesive, which solution is then directly laid over theabove-described substrate or liquid crystal film by an appropriatedeveloping method such as casting or coating or alternatively wherein atacky adhesive layer is formed in accordance with the method asdescribed above on a separator and then transferred onto the liquidcrystal layer. The tacky adhesive layer may contain additives such asnatural or synthetic resins, in particular fillers or pigmentscontaining tackiness-imparting resins, glass fibers, glass beads, metalpowders, and other inorganic powders, dyes, anti-oxidants. The tackyadhesive layer may contain fine particles so as to exhibit lightdiffusivity.

When the homeotropic alignment liquid crystal film formed on a substrateis transferred via a tacky adhesive layer to the stretched film having aretardation function, the homeotropic alignment liquid crystal film maybe subjected to a surface treatment so as to enhance the adhesion to thetacky adhesive layer. There is no particular restriction on the methodof the surface treatment. There may be suitably used a surface treatmentsuch as corona discharge, sputtering, low-pressure UV irradiation, orplasma treatment, which can maintain the transparency of the liquidcrystal film surface. Among these surface treatments, corona dischargetreatment is excellent.

The resulting laminated retardation film may be used in the form of alaminate with an optical film such as a polarizing film.

Alternatively, the laminated retardation film of the present inventionmay be laminated with a cholesteric liquid crystal film so as to form abrightness enhancement film. This brightness enhancement film may beproduced by laminating a polarizer, the laminated retardation filmwherein the stretched film whose Re2 is from 100 to 170 nm, having aretardation function and the homeotropic alignment liquid crystal layerare laminated, and a cholesteric liquid crystal film in this order, andis a linear polarizing film with an extremely large brightness enhancingfunction.

The cholesteric liquid crystal film may be any of those described above.

The laminated retardation film or brightness enhancement film of thepresent invention may be provided with a tacky adhesive layer. The tackyadhesive layer may be used for bonding the film to a liquid crystal cellor for laminating the film with other optical films such as theabove-described retardation film or stretched film. When the opticalfilm is bonded to the laminated retardation film or brightnessenhancement film, the optical axes may be oriented at an appropriateangle depending on the intended retardation characteristics.

There is no particular restriction on the tacky adhesive forming thelayer thereof.

Examples of the tacky adhesive include those used for laminating theabove-described homeotropic alignment liquid crystal film andtransmissive film. The tacky adhesive layer may be provided in the samemanner.

The laminated retardation film and brightness enhancement film of thepresent invention is preferably used for producing various devices suchas liquid crystal display devices and particularly preferably used as aviewing angle improvement film for a liquid crystal display device.

The present invention also provides a viewing angle compensator for avertical alignment type liquid crystal display device, comprising aliquid crystal film comprising a liquid crystalline substance containinga side chain liquid crystalline compound having an oxetanyl group, as aconstituent, aligned homeotropically while the substance is in a liquidcrystal state and fixed in the homeotropic alignment by allowing theoxetanyl group to react.

When the thickness is d1, the main refraction indices in the plane areNx1 and Ny1, the refraction index in the thickness direction is Nz1 andNz1>Nx1≧Ny1 in the homeotropic alignment liquid crystal layer used in aviewing angle compensator for a vertical alignment type liquid crystaldisplay device, the retardation value in the plane (Re1=(Nx1−Ny1)×d1[nm]) is preferably from 0 to 20 nm, and the retardation value in thethickness direction (Rth1=(Nx1−Nz1)×d1 [nm]) is preferably from −500 to−30 nm.

The Re1 and Rth1 values which are optical parameters of the homeotropicalignment liquid crystal layer can not be determined with certaintybecause they depend on the display mode of the liquid crystal displaydevice and various optical parameters. However, with respect to amonochromic light of 550 nm, the retardation value (Re1) in thehomeotropic alignment liquid crystal film plane is adjusted to usuallyfrom 0 nm to 20 nm, preferably from 0 nm to 10 nm, more preferably from0 nm to 5 nm and the retardation value (Rth1) in the thickness directionis adjusted to usually from −500 to −30 nm, preferably −400 to −50 nm,more preferably from −400 to −100 nm.

Adjustment of the Re1 and Rth1 values within the above ranges results ina viewing angle improvement film for a liquid crystal display devicewhich can widen the viewing angle while compensating the color tone ofthe images. When the Re1 value is larger than 20 nm, the frontcharacteristics of the liquid crystal display device would be degradeddue to the large front retardation value. When the Rth1 value is largerthan −30 nm or smaller than −500 nm, sufficient viewing angle improvingeffect may not be attained or unnecessary coloration may occur whenviewing the device obliquely.

Next, a vertical alignment type liquid crystal display device with theviewing angle compensator therefor will be described.

The vertical alignment type liquid crystal display device of the presentinvention comprises a vertical alignment type liquid crystal cellcontaining a pair of substrates each having an electrode and a liquidcrystal molecules to be aligned vertically to the substrate surface whenno electric voltage is applied, arranged between the substrates; twolinear polarizing films arranged above and below the liquid crystalcell; and first optical anisotropic elements exhibiting a retardation of¼ wavelength in the plane, arranged between both surfaces of the liquidcrystal cell and the linear polarizing films, wherein at least oneviewing angle improvement film described above is arranged between thelinear polarizing films and the first optical anisotropic element.

Preferably, between the first optical anisotropic element and theviewing angle improvement film is arranged a second optical anisotropicelement exhibiting a retardation of ½ wavelength in the plane.Preferably, between the first optical anisotropic elements and one orboth surfaces of the liquid crystal cell is arranged at least one thirdoptical anisotropic element having a negative uniaxial opticalanisotropy in the thickness direction. Addition of the third opticalanisotropic element can achieve the wider viewing angle.

There is no particular restriction on the liquid crystal devices to beproduced, which may, therefore, be any of various liquid crystal displaydevices such as transmissive, reflective and transflective liquidcrystal devices. There is no particular restriction on the driving modeof the liquid crystal cell, either, which may, therefore, be a passivematrix mode used in an STN-LCD, an active matrix mode using activeelectrodes such as TFT (Thin Film Transistor) electrodes and TFD (ThinFilm Diode) electrodes, and a plasma address mode.

There is no particular restriction on the transparent substrates formingthe liquid crystal cell as long as they can align a liquid crystallinematerial forming a liquid crystal layer in a specific direction. Morespecific examples include those which themselves have a property ofaligning a liquid crystalline material and those which themselves haveno capability of aligning but are provided with an alignment layercapable of aligning a liquid crystalline material. The electrode of theliquid crystal cell may be any conventional electrode, such as ITO. Theelectrode may be usually arranged on the surface of the transparentsubstrate, which surface contacts the liquid crystal layer. In the caseof using a transparent substrate with an alignment layer, an electrodeis provided between the alignment layer and the transparent substrate.

There is no particular restriction on the liquid crystalline materialforming the liquid crystal layer as long as it is a material exhibitinga negative dielectric anisotropy. Examples of such materials includevarious low molecular weight liquid crystal substances, polymeric liquidcrystal substances, and mixtures thereof, which can form various liquidcrystal cells. The liquid crystalline material may be blended with dyes,chiral dopoants, or non-liquid crystalline substances to an extent thatthey do not prevent the liquid crystal substance from exhibiting liquidcrystallinity. When an electric voltage is applied to the verticalalignment liquid crystal film of a liquid crystal material exhibiting anegative dielectric anisotropy so as to rotate the liquid crystalmolecule, the rotation can be made stable by addition of a chiraldopant. Furthermore, when the rubbing directions of the upper and lowersubstrates are arranged in a direction other than the same direction,streaking is hard to be visible because the orbit of the alignment willnot be in the same direction. When the liquid crystal layer is twistedat 90 degrees, retardation occurs in the tilt direction of the liquidcrystal molecules when are aligned, tilted at a few degrees to thesubstrates for preventing disclination upon application of an electricvoltage. However, since the directions of the liquid crystal moleculesnear the substrates form an angle of 90 degrees near the upper and lowersubstrates, the disclination can be cancelled, leading to a black imagewith less leak light.

The two linear polarizing films arranged above and below the verticalalignment liquid crystal cell are usually those having a protection filmon one or both surfaces of the polarizers.

A circular polarizing film can be formed by combining the linearpolarizing film and a ¼ wavelength plate. The circular polarizing filmhas a function to change a linearly polarized light to a circularlypolarized light or a circularly polarized light to a linearly polarizedlight due to the presence of the ¼ wavelength plate.

Presence of the linearly polarizing films arranged on both surfaces ofthe vertical alignment liquid crystal cell and the first opticalanisotropic elements having a retardation of ¼ wavelength in the plane,arranged between the linear polarizing films and the vertical alignmentliquid crystal cell allows for display of dark image by crossing theupper and lower polarizing films because the retardation in the viewingdirection of the liquid crystal becomes zero when no electric voltage isapplied and allows for display of bright image because the retardationin the viewing angle occurs when an electric voltage is applied. In thiscase, because the angle defined by the slow axis of the first opticalanisotropic element having a retardation of ¼ wavelength and theabsorption axis of the linear polarizing film is 45 degrees, it isrendered possible to make an incident of circularly polarized light tothe liquid crystal layer with the most simple structure.

In the case of a transflective vertical alignment type liquid crystaldisplay device provided with both transmission and reflectioncapabilities, it is preferred to use a first optical anisotropic elementhaving a retardation of ¼ wavelength in the whole wavelength or use asecond optical anisotropic element having a retardation of ½ wavelengthin the plane, between the linear polarizing film and the ¼ wavelengthplate.

Next, the first and second optical anisotropic elements having aretardation of ¼ wavelength and a retardation of ½ wavelength in theplane, respectively will be described.

Examples of these optical anisotropic elements include birefringencefilms obtained by uniaxially or biaxially stretching films formed fromappropriate polymers such as polycarbonates, norbornene resins,polyvinyl alcohols, polystyrenes, polymethyl methacrylates,polypropylenes, other polyolefins, polyarylates, and polyamides or by amethod as disclosed in Japanese Patent Laid-Open Publication No 5-157911wherein such polymer films of an elongate form, with a heat contractivefilm attached thereto are heat-contracted with the action thereof in thewidth direction so as to increase the retardation in the thicknessdirection; aligned films formed from liquid crystal materials such asliquid crystal polymers; and aligned layers of liquid crystal materialssupported on a film.

When the x axis and y axis directions are defined in the plane and thethickness direction is defined as z, a positive uniaxial opticalanisotropic element has a refractive index defined by nx>ny=nz. Apositive biaxial anisotropic element has a refractive index defined bynz>nx>ny. A negative uniaxial optical anisotropic element has arefractive index defined by nx=ny>nz. A negative biaxial anisotropicelement has a refractive index defined by nx>ny>nz.

When the biaxiality is defined by NZ coefficient=(nx−nz)/(nx−ny), NZ>1,NZ=1, and NZ<1 can be classified into negative biaxiality, positiveuniaxiality, and positive biaxiality, respectively.

When the thickness is d2, the main refractive indices in the plane areNx2 and Ny2, the main refractive index in the thickness direction isNz2, and Nx2>Ny2 in the first optical anisotropic element having aretardation of ¼ wavelength in the plane, the element has a retardationvalue in the plane (Re2=(Nx2−Ny2)×d2 [nm]) of 80 to 170 nm and arelationship defined by −1<NZ2<4 when the NZ coefficient of the elementis NZ2.

The Re2 and NZ2 values which are optical parameters of the first opticalanisotropic element can not be determined with certainty because theydepend on the display mode of the liquid crystal display device andvarious optical parameters. However, with respect to a monochromic lightof 550 nm, the retardation value (Re2) in the first optical anisotropicelement plane is adjusted to usually from 80 nm to 170 nm, preferablyfrom 100 nm to 150 nm, more preferably from 120 nm to 140 nm and the NZ2value is adjusted to usually −1<NZ2<4, preferably 0.5<NZ2<3, morepreferably 1≦NZ2<3.

When the thickness is d3, the main refractive indices in the plane areNx3 and Ny3, the main refractive index in the thickness direction isNz3, and Nx3>Ny3 in the second optical anisotropic element having aretardation of ½ wavelength in the plane, the element has a retardationvalue in the surface (Re3=(Nx3−Ny3)×d3 [nm]) of 200 to 350 nm and arelationship defined by −1<NZ3<4 when the NZ coefficient of the elementis NZ3.

The Re3 and NZ3 values, which are optical parameters of the secondoptical anisotropic element can not be determined with certainty becausethey depend on the display mode of the liquid crystal display device andvarious optical parameters. However, with respect to a monochromic lightof 550 nm, the retardation value (Re3) in the second optical anisotropicelement plane is adjusted to usually from 200 nm to 350 nm, preferablyfrom 250 nm to 300 nm, more preferably from 260 nm to 280 nm and the NZ3value is adjusted to usually −1<NZ3<4, preferably −1<NZ3<2, morepreferably 0≦NZ3<1.5.

Adjustment of the Re2 and Re3 values and NZ2 and NZ3 values within theabove ranges results in a viewing angle improvement film for a liquidcrystal display device which can widen the viewing angle whilecompensating the color tone of the images. When the Re2 and Re3 valuesdeviated from the above ranges, the front characteristics of the liquidcrystal display device would be degraded due to the deviance of thefront retardation value. When the NZ2 and NZ3 values deviate from theabove ranges, sufficient viewing angle improving effect may not beattained or unnecessary coloration may occur when viewing the deviceobliquely.

Next, the third optical anisotropic element having a negative opticalanisotropy in the thickness direction will be described.

There is no particular restriction on the third optical anisotropicelement. The third optical anisotropic element may be formed from anon-liquid crystalline material or a liquid crystalline material.Preferred examples of the non-liquid crystalline material includepolymers, for example, cellulose triacylate, polyolefins such as ZEONEXand ZEONOR (manufactured by ZEON CORPORATION) and ARTON (manufactured byJSR Corporation), polyamides, polyimides, polyesters, polyetherketones,polyaryletherketones, polyamideimides, and polyesterimides because oftheir excellent heat resistance, chemical resistance, transparency, andrigidity. These polymers may be used alone or in combination.Alternatively, these polymers may be used in the form of a mixture oftwo or more of these polymers having different functional groups fromeach other, such as polyaryletherketone and polyamide. Among thesepolymers, particularly preferred are polyimides because of their hightransparency and alignability. Examples of the liquid crystallinematerial include cholesterically aligned film formed from liquid crystalmaterials such as cholesteric liquid crystal polymers andcholesterically aligned layers of liquid crystal materials supported ona film.

When the thickness is d4, the main refractive indices in the plane areNx4 and Ny4, the main refractive index in the thickness direction isNz4, and Nx4>Ny4 in the third optical anisotropic element, the elementhas a retardation value in the plane (Re4=(Nx4−Ny4)×d4 [nm]) ofpreferably from 0 to 20 nm and a retardation value in the thicknessdirection (Rth4=(Nx4−Nz4)×d4 [nm]) of preferably from 50 to 500 nm.

The Re4 and Rth4 values, which are optical parameters of the thirdoptical anisotropic element can not be determined with certainty becausethey depend on the display mode of the liquid crystal display device andvarious optical parameters. However, with respect to a monochromic lightof 550 nm, the retardation value (Re4) in the third optical anisotropicelement plane is adjusted to usually from 0 nm to 20 nm, preferably from0 nm to 10 nm, more preferably from 0 nm to 5 nm and the retardationvalue (Rth4) in the thickness direction is adjusted to usually from 50to 500 nm, preferably 80 to 400 nm, more preferably from 100 to 300 nm.

Adjustment of the Re4 and Rth4 values within the above ranges results ina viewing angle improvement film for a liquid crystal display devicewhich can widen the viewing angle while compensating the color tone ofthe images. When the Re4 value is larger than 20 nm, the frontcharacteristics of the liquid crystal display device would be degradeddue to the large front retardation value. When the Rth4 value is smallerthan 50 nm or larger than 500 nm, sufficient viewing angle improvingeffect may not be attained or unnecessary coloration may occur whenviewing the device obliquely.

The first, second and third optical anisotropic elements and thehomeotropic alignment liquid crystal film may be laminated to each othervia a tacky adhesive layer. Alternatively, after the homeotropicalignment liquid crystal film formed on a substrate may be transferredvia a tacky adhesive layer to the first or second optical anisotropicelement, the third optical anisotropic element which has not been usedmay be further laminated thereto via a tacky adhesive layer.

When the homeotropic alignment liquid crystal film formed on a substrateis transferred via a tacky adhesive layer to the first or second opticalanisotropic element, the homeotropic alignment liquid crystal film maybe subjected to a surface treatment so as to enhance the adhesion to thetacky adhesive layer. There is no particular restriction on the methodof the surface treatment. There may be suitably used a surface treatmentsuch as corona discharge, sputtering, low-pressure UV irradiation, orplasma treatment, which can maintain the transparency of the liquidcrystal film surface. Among these surface treatments, corona dischargetreatment is excellent.

One of the substrates of the above-described vertical alignment typeliquid crystal cell may be changed to a substrate having a region withreflectivity and a region with transmissivity thereby obtaining atransflective vertical alignment type liquid crystal display device.

There is no particular restriction on the region with reflectivity(hereinafter may be referred to as “reflection region”) contained in thetransflective electrode, which may, therefore, be a metal such asaluminum, silver, gold, chromium, and platinum, an alloy containing oneor more of these metals, an oxide such as magnesium oxide, amulti-layered film of dielectrics, a liquid crystal film exhibiting aselective reflectivity, and combinations thereof. These reflectionlayers may be flat or curved and may be those provided with diffusivereflectivity by forming irregularity on its surface, those having afunction as the electrode on the electrode substrate located on the sideopposite to the viewing side, or any combination thereof.

The vertical alignment type liquid crystal display device of the presentinvention may be provided with components other than those describedabove. For example, the use of a color filter makes it possible toproduce a color liquid crystal display which can provide multi- orfull-colored images with increased color purity.

Next, the organic electroluminescence device (organic EL display device)of the present invention will be described. In general, an EL displaydevice comprises an illuminant (organic electroluminescent illuminant)formed by laminating a transparent electrode, an organic illuminationlayer, and a metal electrode in this order on a transparent substrate.The organic illumination layer is a laminate of various organic filmsand for example is known to be of various structures such as a laminateof a hole injection layer of a triphenylamine derivative and anillumination layer of a fluorescent organic solid such as anthracene; alaminate of such an illumination layer and an electron injection layerof a perylene derivative, and a laminate of such a hole injection layer,an illumination layer, and an electron injection layer.

The organic EL display device illuminates on the basis of the principlethat when an electric voltage is applied to the transparent electrodeand the metal electrode, causing holes and electrons to be injected tothe organic illumination layer, the energy generated by the re-couplingof the holes and electrons excites the fluorescent substance and a lightis illuminated when the excited fluorescent substance returns to aground state. The re-coupling is the same in mechanism as an ordinarydiode. As anticipated from this, the current and luminescence intensityexhibit strong non-linearity accompanying rectification characteristicsto the applied electric voltage.

In the organic EL display device, at least one of the electrodes must betransparent in order to take out the light illuminated in the organicillumination layer, and thus a transparent electrode formed from atransparent conductive material such as Indium Tin Oxide (ITO) isusually used as an anode. While, since it is important to use asubstance which is small in work function for a cathode in order to makethe injection of electrons easy and thus increase the illuminationefficiency, a metal electrode such as Mg—Ag and Al—Li is used.

In the organic EL display device with the above-described structure, theorganic illumination layer is formed of an extremely thin film with athickness of on the order of 10 nm. The organic illumination layer thusalso transmits light substantially completely, similarly to thetransparent electrode. Consequently, since during the non-illuminationmode, the light made incident through the transparent substratetransmits through the transparent electrode and organic illuminationlayer, and then reflects at the metal electrode and then appears on thesurface of the transparent substrate again, the displaying surface ofthe organic EL display device look like a mirror when viewed from theoutside.

In the organic EL display device wherein the organic illumination layerilluminating upon application of an electric voltage is provided with onits top surface with a transparent electrode and on its bottom surfacewith a metal electrode, a polarizing film may be provided on the topsurface side of the transparent electrode, and a retardation film may beprovided between the transparent electrode and the polarizing film.

The retardation film and polarizing film has an action to polarize alight externally made incident and reflected at the metal electrode andthus an effect not to make the mirror surface of the metal electrodevisible with the action. In particular, when the retardation film isformed with a ¼ wavelength plate and the angle formed by thepolarization directions of the polarizing film and retardation film isadjusted to π/4, the mirror surface of the metal electrode can becompletely shielded.

That is, for the environment light made incident to the organic ELdisplay device, only the linearly polarized component transmitstherethrough due to the presence of the polarizer. This linearlypolarized light becomes an elliptically polarized light due to thepresence of the retardation film but becomes a circularly polarizedlight in particular when the retardation film is a ¼ wavelength plateand the angle formed by the polarization directions of the polarizingfilm and retardation film is adjusted to π/4.

The circularly polarized light becomes a linearly polarized light againat the retardation film after transmitting through the transparentsubstrate, transparent electrode, and organic thin film, reflected atthe metal electrode and transmitting through the organic thin film,transparent electrode, and transparent substrate. The linearly polarizedlight crosses with the polarization direction of the polarizing film andthus can not transmit therethrough. As the result, the mirror surface ofthe metal electrode can be completely shielded.

The polarizing film containing the homeotropic alignment liquid crystalfilm of the present invention can be suitably used for the organic ELdisplay device.

Applicability in the Industry

The present invention can provide a homeotropic alignment liquid crystalfilm with excellent heat resistance, high rigidity, and excellentmechanical strength, produced by fixing a liquid crystal materialcontaining a side chain liquid crystalline polymeric compound obtainedby polymerizing a novel (meth)acrylic compound having an oxetanyl group,in an aligned state. The liquid crystal film can be used as an opticalfilm for various image displaying devices such as liquid crystal displaydevices, organic EL display devices, and PDP.

Best Mode for Carrying out the Present Invention

The present invention will be further described in the followingexamples, but the present invention should not be construed as beinglimited thereto.

The analyzing methods used in the examples are as follows.

-   (1) ¹H-NMR measurement

A compound was dissolved in deuterated chloroform and was determined bymeans of ¹H-NMR at 400 MHz (INOVA-400 manufactured by Varinat Co.,Ltd.).

-   (2) GPC measurement

The GPC measurement was carried out to determine the number-averagemolecular weight (Mn) and weight-average molecular weight (Mw) of aliquid crystalline polymer by dissolving the compound in tetrahydrofuranand using 8020 GPC system manufactured by TOSOH CORPORATION equippedwith TSK-GEL, Super H1000, Super H2000, Super H3000, and Super H4000which are connected in series and tetrahydrofuran as an eluent solvent.Polystyrene was used as a standard for calibration of the molecularweight.

-   (3) Observation through Microscope

The liquid crystal aligned state was observed using an Olympus BH2polarizing microscope.

-   (4) Parameter measurement of liquid crystal film    The measurement was carried out using an automatic birefringence    analyzer KOBRA21ADH manufactured by Oji Scientific Instruments.

EXAMPLE 1

A liquid crystalline polymer represented by formula (8) below wassynthesized by radical polymerization. With regard to the molecularweight in terms of polystyrene, Mn=8000 and Mw=15000. The representationin formula (8) indicates the structural ratio of the monomer but doesnot mean a block copolymer. The same is also applied to formulas (9)through (13) below.

In 9 ml of cyclohexanone was dissolved 1.0 g of the polymer of formula(8), followed by addition of 0.1 g of a propylene carbonate solution of50 percent of triarylsulfonium hexafluoroantimonate (a reagentmanufactured by Aldrich Co.) at a dark place and filtration ofinsolubles with a polytetrafluoroethylene filter with a pore size of0.45 μm thereby obtaining a liquid crystal material solution.

An alignment substrate was prepared as follows.

A polyethylene terephthalate film with a thickness of 38 μm(manufactured by Toray Industries Inc.) was cut into a size of 15 cmsquare and spin-coated with a solution of 5 percent by weight of analkyl-modified polyvinyl alcohol (MP-203 manufactured by KURARAY CO.,LTD.) (solvent is a mixed solvent of water and isopropyl alcohol at aweight ratio of 1:1). The coated film was dried on a hot plate kept at50° C. for 30 minutes and heated at 120° C. in an oven for 10 minutes.The thickness of the resulting PVA layer was 1.2 μm. The PVA layer wasrubbed with a rayon cloth. The peripheral velocity ratio (the movingvelocity of the rubbing cloth/the moving velocity of the substrate film)was set to 4.

On the resulting alignment substrate was spin-coated the liquid crystalmaterial solution obtained above. The coated alignment substrate wasdried on a hot plate kept at 60° C. for 10 minutes and heated at 150° C.in an oven for 2 minutes thereby aligning the liquid crystal material.The sample was placed on an aluminum plate heated at 60° C., makingcontact therewith and irradiated with an ultraviolet light of 600 mJ/cm²(measured at 365 nm) using a high pressure mercury lamp thereby curingthe liquid crystal material.

Since the polyethylene terephthalate film used as a substrate was largein birefringence and thus not preferable for an optical film, theresulting liquid crystal film (cured liquid crystal material layer) onthe alignment substrate was transferred via an ultraviolet curing typeadhesive onto a triacetylcellulose (TAC) film. More specifically, theadhesive with a thickness of 5 μm was coated over the cured liquidcrystal material layer on the polyethylene terephthalate film andlaminated with a TAC film. After the laminate was subjected to anirradiation of ultraviolet light from the TAC film side so as to curethe adhesive, the polyethylene terephthalate film was released.

As a result of observation of the resulting optical film (PVAlayer/liquid crystal layer/adhesive layer/TAC film) through a polarizingmicroscope, it was confirmed that the film was aligned in a monodomainuniform aligned state having no disclination. As result of observationof the optical film through a conoscope, it was confirmed that thealignment was a homeotropic alignment having a positive uniaxialrefraction structure. As the result of measurement using KOBRA21ADH, thecombination of the TAC film and the liquid crystal layer was found tohave a retardation in the plane direction (Re) of 0.5 nm and aretardation in the thickness direction (Rth) of −150 nm. The TAC filmitself had a negative uniaxiality and a retardation in the plane of −0.5nm and a retardation in the thickness direction of +40 nm. Therefore, itwas assessed that the liquid crystal layer itself had an Re of 0 nm andan Rth of −190 nm.

Furthermore, only the liquid crystal material portion was scrapped offfrom the optical film and the glass transition temperature thereof wasmeasured using a DSC. As a result, it was found to be 100° C. The pencilhardness of the liquid crystal material surface of the film was on theorder of 2H and thus it was confirmed that the film had a sufficienthardness.

EXAMPLE 2

A liquid crystalline polymer represented by formula (9) below wassynthesized by radical polymerization. With regard to the molecularweight in terms of polystyrene, Mn=6000 and Mw=12000.

A low molecular weight liquid crystalline compound having an oxetanylgroup represented by formula (10) was synthesized.

In 9 ml of diethylene glycol dimethyl ether were dissolved 0.8 g of thepolymer of formula (9) and 0.2 g of the compound of formula (10),followed by addition of 0.1 g of a propylene carbonate solution of 50percent of triarylsulfonium hexafluoroantimonate (a reagent manufacturedby Aldrich Co.) and a slight amount of a fluorine-based surfactant at adark place and filtration of insolubles with a polytetrafluoroethylenefilter with a pore size of 0.45 μm thereby preparing a liquid crystalmaterial solution.

An alignment substrate was prepared as follows.

A polyethylene naphthalate film with a thickness of 50 μm (manufacturedby Teijin Dupont Films Japan Ltd.) was cut into a size of 15 cm squareand spin-coated with a solution of 5 percent by weight of analkyl-modified polyvinyl alcohol (MP-102 manufactured by KURARAY CO.,LTD.) (solvent is a mixed solvent of water and isopropyl alcohol at aweight ratio of 1:1). The coated film was dried on a hot plate kept at50° C. for 30 minutes and heated at 150° C. in an oven for 5 minutes.The thickness of the resulting PVA layer was 0.8 μm. The PVA layer wasrubbed with a rayon cloth. The peripheral velocity ratio (the movingvelocity of the rubbing cloth/the moving velocity of the substrate film)was set to 10.

On the resulting alignment substrate was spin-coated the liquid crystalmaterial solution obtained above. The coated alignment substrate wasdried on a hot plate kept at 60° C. for 10 minutes and heated at 150° C.in an oven for 2 minutes thereby aligning the liquid crystal material.The sample was placed on an aluminum plate heated at 60° C., makingcontact therewith and irradiated with an ultraviolet light of 400 mJ/cm²(measured at 365 nm) using a high pressure mercury lamp thereby curingthe liquid crystal material.

Since the polyethylene naphthalate film used as a substrate was large inbirefringence and thus not preferable for an optical film, the resultingliquid crystal film on the alignment substrate was transferred via anultraviolet curing type adhesive onto a polycarbonate film having aretardation of 140 nm in the plane direction. More specifically, theadhesive with a thickness of 5 μm was coated over the cured liquidcrystal material layer on the polyethylene naphthalate film andlaminated with a polycarbonate film. After the laminate was subjected toan irradiation of ultraviolet light from the polycarbonate film side soas to cure the adhesive, the PVA layer and polyethylene naphthalate filmwere released.

The resulting optical film (liquid crystal layer/adhesivelayer/polycarbonate film) had a retardation in the plane (Re) of 140 nmand biaxiality. The liquid crystal layer itself was estimated to have anRth of −120 when it was transferred to a TAC film having no anisotropyin the plane, as done in Example 1.

Two sheets of this liquid crystal film formed on the polycarbonate filmwere each arranged in a commercially available IPS type liquid crystaltelevision so as to be positioned between the upper polarizing film andthe cell and between the lower polarizing film and the cell. As theresult, it was found that the viewing angle was enlarged and a moreexcellent image was provided even when the television was viewedobliquely, compared with an IPS type television without the liquidcrystal film.

As shown in FIG. 1, one sheet of this liquid crystal film formed on thepolycarbonate film (optical film: homeotropic alignment liquid crystalfilm b and polycarbonate film c) was arranged in a commerciallyavailable IPS type liquid crystal television wherein a backlight f, alower polarizing film e, an IPS type liquid crystal cell d, and an upperpolarizing film a are laminated in this order, so as to be positionedbetween the upper polarizing film a and the liquid crystal cell d. Asthe result, it was found that the viewing angle was enlarged and a moreexcellent image was provided even when the television was viewedobliquely, compared with an IPS type television without the opticalfilm.

EXAMPLE 3

A liquid crystalline polymer represented by formula (11) below wassynthesized. With regard to the molecular weight in terms ofpolystyrene, Mn=11000 and Mw=20000.

In 9 ml of cyclohexanone was dissolved 1.0 g of the polymer of formula(11), followed by addition of 0.05 g of a photo initiator SP-172manufactured by ADEKA CORPORATION at a dark place and filtration ofinsolubles with a polytetrafluoroethylene filter with a pore size of0.45 μm thereby preparing a liquid crystal material solution.

An alignment substrate was prepared as follows.

An N-methylpyrrolidone solution of 5 percent by weight of polyamide(η=0.4) represented by formula (12) below was spin-coated on a 0.7 mmthickness borosilicate glass of 15 cm square. The coated glass was driedon a hot plate kept at 80° C. for 30 minutes and heated at 120° C. in anoven for 10 minutes.

On the resulting alignment substrate was spin-coated the liquid crystalmaterial solution obtained above. The coated alignment substrate wasdried on a hot plate kept at 60° C. for 10 minutes and heated at 140° C.in an oven for 2 minutes thereby aligning the liquid crystal material.The sample was placed on an aluminum plate heated at 70° C., makingcontact therewith and irradiated with an ultraviolet light of 300 mJ/cm²(measured at 365 nm) using a high pressure mercury lamp thereby curingthe liquid crystal material.

As a result of observation of the resulting optical film on the glasssubstrate through a polarizing microscope, it was confirmed that thefilm was aligned in a monodomain uniform homeotropic liquid crystalalignment having no disclination. The retardation (Rth) measured usingKOBRA21ADH was −250 nm.

EXAMPLE 4

On a cholesteric liquid crystal layer (thickness: 5 μm) exhibiting acircularly polarized dichroism in a spectrum of 400 to 700 nm, formed ona TAC film (thickness: 80 μm) was laminated the homeotropic alignmentliquid crystal film obtained in Example 3 via a tacky adhesive layer(thickness: 25 μm) of an acrylic tacky adhesive. On the liquid crystalfilm was laminated a ¼ wavelength plate (retardation in the plane: 130nm) (thickness: 60 μm) produced by stretching a polycarbonate film via atacky adhesive layer (thickness: 25 μm) of the same acrylic tackyadhesive thereby producing a brightness enhancement film.

As shown in FIG. 2, the resulting brightness enhancement film n(cholesteric liquid crystal film m, homeotropic alignment liquid crystalfilm k, ¼ wavelength plate j) was arranged in a commercially availableliquid crystal display wherein a backlight v, a lower polarizing film i,a liquid crystal cell h, and an upper polarizing film g were laminatedin this order, so as to be positioned between the backlight v and thelower polarizing film i. As a result, it was found that a bright imageenhanced by 30 percent was provided, compared with a liquid crystaldisplay device with no brightness enhancement film n.

EXAMPLE 5

An alignment substrate was prepared as follows.

A polyethylene terephthalate film with a thickness of 38 μm(manufactured by Toray Industries Inc.) was cut into a size of 15 cmsquare and spin-coated with a solution of 5 percent by weight of analkyl-modified polyvinyl alcohol (MP-203 (PVA) manufactured by KURARAYCO., LTD.) (solvent is a mixed solvent of water and isopropyl alcohol ata weight ratio of 1:1). The coated film was dried on a hot plate kept at50° C. for 30 minutes and heated at 120° C. in an oven for 10 minutes.The PVA layer was rubbed with a rayon cloth. The thickness of theresulting PVA layer was 1.2 μm. The peripheral velocity ratio (themoving velocity of the rubbing cloth/the moving velocity of thesubstrate film) was set to 4.

On the resulting alignment substrate was spin-coated the liquid crystalmaterial solution prepared in Example 1. The coated alignment substratewas dried on a hot plate kept at 60° C. for 10 minutes and heated at150° C. in an oven for 2 minutes thereby aligning the liquid crystalmaterial. The sample was placed on an aluminum plate heated at 60° C.,making contact therewith and irradiated with an ultraviolet light of 600mJ/cm² (measured at 365 nm) using a high pressure mercury lamp therebycuring the liquid crystal material (thickness of the homeotropicalignment liquid crystal layer: 0.8 μm).

Since the polyethylene terephthalate film used as a substrate was largein birefringence and thus not preferable for an optical film, theresulting liquid crystal film on the alignment substrate was transferredvia an ultraviolet curing type adhesive onto a triacetylcellulose (TAC)film. More specifically, the adhesive with a thickness of 5 μm wascoated over the cured liquid crystal material layer on the polyethylenenaphthalate film and laminated with a TAC film. After the laminate wassubjected to an irradiation of ultraviolet light from the TAC film sideso as to cure the adhesive, the polyethylene terephthalate film wasreleased.

As a result of observation of the resulting optical film (PVAlayer/liquid crystal layer/adhesive layer/TAC film) through a crossednicols polarizing microscope, it was confirmed that the film was alignedin a monodomain uniform aligned state having no disclination. As aresult of observation of the optical film through a conoscope, it wasconfirmed that the alignment was a homeotropic alignment having apositive uniaxial refraction structure. As a result of similarobservation through a crossed nicols polarizing microscope of the filmwhich was tilted and to which a light was made incident obliquely, itwas confirmed that the light transmitted through the film. The opticalretardation of the film was measured using KOBRA21ADH. A measuring lightwas made incident vertically or obliquely to the sample surface toobtain a chart of the optical retardation and incident angle of themeasuring light. It was confirmed from the chart that the film wasaligned homeotropically. In the homeotropic alignment, the retardationin the vertical direction to the sample surface (front retardation) issubstantially zero. When the retardation of this sample was measuredfrom an oblique direction to the slow axis direction of the liquidcrystal layer, it was able to be determined that a homeotropic alignmentwas formed because the retardation value increases as the incident angleof the measuring light increases. From the foregoing, it was assessedthat the homeotropic alignability of the liquid crystal layer wasexcellent.

The Nx1, Ny1 and Nz1 of the homeotropic alignment liquid crystal filmwere 1.54, 1.54 and 1.73, respectively.

Furthermore, only the liquid crystal material portion was scrapped offfrom the laminated film and the glass transition temperature thereof wasmeasured using a DSC. As a result, it was found to be 100° C. The pencilhardness of the liquid crystal material surface of the film was on theorder of 2H and thus it was confirmed that the film had a sufficienthardness.

The liquid crystal layer on the alignment substrate was transferred viaan ultraviolet curing type adhesive onto a retardation film produced bystretching a polycarbonate film having a retardation in the planedirection of 140 nm (manufactured by Sumitomo Chemical Co., Ltd.,thickness: 40 μm, Nx2: 1.5930, Ny2: 1.5887, Nz2: 1.5883). Morespecifically, the adhesive was coated over the cured liquid crystalmaterial layer on the polyethylene terephthalate film and laminated witha polycarbonate film. After the laminate was subjected to an irradiationof ultraviolet light of 400 mJ/cm² from the polycarbonate film side soas to cure the adhesive, the PVA layer and polyethylene terephthalatefilm were released thereby obtaining a laminated retardation filmwherein the homeotropic alignment liquid crystal layer and thepolycarbonate stretched film were laminated according to the presentinvention.

The resulting laminated retardation film (homeotropic alignment liquidcrystal film/adhesive layer/polycarbonate film) had a retardation in theplane (Re3) of 140 nm and biaxiality.

As shown in FIG. 1, one sheet of this laminated retardation film wasarranged in a commercially available IPS type liquid crystal televisionwherein a backlight, a lower polarizing film, an IPS type liquid crystalcell, and an upper polarizing film are laminated in this order, so as tobe positioned between the upper polarizing film and the liquid crystalcell. As the result, it was found that the viewing angle was enlargedand a more excellent image was provided even when the television wasviewed obliquely, compared with an IPS type television without thelaminated retardation film.

EXAMPLE 6

An alignment substrate was prepared as follows.

A retardation film produced by stretching a polycarbonate film having aretardation in the plane direction of 140 nm (manufactured by SumitomoChemical Co., Ltd., thickness: 40 μm, Nx2: 1.5930, Ny2: 1.5887, Nz2:1.5883) was cut into a size of 15 cm square and spin-coated with asolution of 5 percent by weight of an alkyl-modified polyvinyl alcohol(MP-203 (PVA) manufactured by KURARAY CO., LTD.) (solvent is a mixedsolvent of water and isopropyl alcohol at a weight ratio of 1:1). Thecoated film was dried on a hot plate kept at 50° C. for 30 minutes andheated at 120° C. in an oven for 10 minutes. The PVA layer was rubbedwith a rayon cloth. The thickness of the resulting PVA layer was 1.2 μm.The peripheral velocity ratio (the moving velocity of the rubbingcloth/the moving velocity of the substrate film) was set to 4.

On the resulting alignment substrate was spin-coated the liquid crystalmaterial solution prepared in Example 1. The coated alignment substratewas dried on a hot plate kept at 60° C. for 10 minutes and heated at150° C. in an oven for 2 minutes thereby aligning the liquid crystalmaterial. The sample was placed on an aluminum plate heated at 60° C.,making contact therewith and irradiated with an ultraviolet light of 600mJ/cm² (measured at 365 nm) using a high pressure mercury lamp so as tocure the liquid crystal material (the thickness of the homeotropicalignment liquid crystal layer: 0.8 μm) thereby obtaining a laminatedretardation film wherein the homeotropic alignment liquid crystal filmand the polycarbonate stretched film were laminated according to thepresent invention.

In order to confirm that the resulting liquid crystal layer formed anexcellent homeotropic alignment, the liquid crystal layer on the liquidcrystal layer/PVA layer/polycarbonate stretched film was transferred viaan ultraviolet curing type adhesive onto a TAC film. More specifically,the adhesive with a thickness of 5 μm was coated over the cured liquidcrystal material layer on the PVA layer and laminated with a TAC film.After the laminate was subjected to an irradiation of ultraviolet lightfrom the TAC film side so as to cure the adhesive, the PVA/polycarbonatestretched film were released.

As a result of observation of the resulting laminated film (liquidcrystal layer/adhesive layer/TAC film) through a crossed nicolspolarizing microscope, it was confirmed that the film was aligned in amonodomain uniform aligned state having no disclination. As a result ofobservation of the optical film through a conoscope, it was confirmedthat the alignment was a homeotropic alignment having a positiveuniaxial refraction structure. As a result of similar observationthrough a crossed nicols polarizing microscope of the film which wastilted and to which a light was made incident obliquely, it wasconfirmed that the light transmitted through the film. The opticalretardation of the film was measured using KOBRA21ADH. A measuring lightwas made incident vertically or obliquely to the sample surface toobtain a chart of the optical retardation and incident angle of themeasuring light. It was confirmed from the chart that the film wasaligned homeotropically. In the homeotropic alignment, the retardationin the vertical direction to the sample surface (retardation in theplane) is substantially zero. When the retardation of this sample wasmeasured from an oblique direction to the slow axis direction of theliquid crystal layer, it was able to be determined that the homeotropicalignment was formed because the retardation value increases as theincident angle of the measuring light increases. From the foregoing, itwas assessed that the homeotropic alignability of the liquid crystallayer was excellent.

The Nx1, Ny1 and Nz1 of the homeotropic alignment liquid crystal filmwere 1.54, 1.54 and 1.73, respectively.

Furthermore, only the liquid crystal material portion was scrapped offfrom the laminated film and the glass transition temperature thereof wasmeasured using a DSC. As a result, it was found to be 100° C. The pencilhardness of the liquid crystal material surface of the film was on theorder of 2H and thus it was confirmed that the film had a sufficienthardness.

The resulting laminated retardation film (homeotropic alignment liquidcrystal layer/PVA layer/polycarbonate film) had a retardation in theplane (Re3) of 140 nm and biaxiality.

As shown in FIG. 1, one sheet of this laminated retardation film wasarranged in a commercially available IPS type liquid crystal televisionwherein a backlight, a lower polarizing film, an IPS type liquid crystalcell, and an upper polarizing film are laminated in this order, so as tobe positioned between the upper polarizing film and the liquid crystalcell. As the result, it was found that the viewing angle was enlargedand more excellent images was provided even when the television wasviewed obliquely, compared with an IPS type television without the filmsimilarly to Example 1.

EXAMPLE 7

On a 5 μm thick cholesteric liquid crystal layer exhibiting a circularlypolarized dichroism in a spectrum of 400 to 700 nm, formed on a TAC film(thickness: 80 μm) was laminated a 50 μm thickness retardation filmwherein the homeotropic alignment liquid crystal film obtained inExample 1 and a retardation film of a polycarbonate stretched film(front retardation: 140 nm) via a tacky adhesive layer (thickness: 25μm) of an acrylic tacky adhesive thereby preparing a brightnessenhancement film according to the present invention.

As shown in FIG. 2, the resulting brightness enhancement film wasarranged in a commercially available liquid crystal display wherein abacklight, a lower polarizing film, a liquid crystal cell, and an upperpolarizing film are laminated in this order, so as to be positionedbetween the backlight and the lower polarizing film. As a result, it wasfound that a bright image enhanced by 30 percent was provided, comparedwith a liquid crystal display device with no brightness enhancementfilm.

COMPARATIVE EXAMPLE 1

A solution was prepared by dissolving 5 parts by weight of a side chainliquid crystal polymer represented by formula (13) below (indicated inblock polymer form for convenience, the numerals in the formula indicatethe mol % of the monomer units, weight-average molecular weight: 5000),20 parts by weight of a photo polymerizable liquid crystal compoundexhibiting a nematic liquid crystal phase (Paliocolor LC242 manufacturedby BASF Ltd.) and 5 parts by weight (the ratio based on the photopolymerizable liquid crystal compound) of a photo polymerizationinitiator (IRGACURE 907 manufactured by Ciba Specialty Chemicals) in 75parts by weight of cyclohexanone. The solution was filtered to removeinsolubles with a polytetrafluoroethylene filter with a pore size of0.45 μm thereby preparing a liquid crystal material solution.

The resulting liquid crystal solution was spin-coated on an alignmentsubstrate produced similarly in Example 1. The coated substrate washeated at 80° C. for 2 minutes and then cooled immediately to the roomtemperature thereby aligning homeotropically the liquid crystal materiallayer and vitrifying the layer, maintaining the alignment so as to fixthe homeotropic alignment liquid crystal layer. The fixed homeotropicalignment liquid crystal layer was irradiated with an ultraviolet lightthereby forming a homeotropic alignment liquid crystal film (thickness:1.0 μm).

Only the liquid crystal material portion of the resulting homeotropicalignment liquid crystal film was scrapped off and the glass transitiontemperature thereof was measured using a DSC. As a result, it was foundto be 80° C. The pencil hardness of the liquid crystal material surfaceof the film was on the order of 2 B and thus it was confirmed that thefilm had a low hardness.

EXAMPLE 8

An alignment substrate was prepared as follows.

A 38 μm thick polyethylene naphthalate film (manufactured by TorayIndustries Inc.) was cut into a size of 15 cm square and spin-coatedwith a solution of 5 percent by weight of an alkyl-modified polyvinylalcohol (MP-203 manufactured by KURARAY CO., LTD.) (solvent is a mixedsolvent of water and isopropyl alcohol at a weight ratio of 1:1). Thecoated film was dried on a hot plate kept at 50° C. for 30 minutes andheated at 120° C. in an oven for 10 minutes. The PVA layer was rubbedwith a rayon cloth. The thickness of the resulting PVA layer was 1.2 μm.The peripheral velocity ratio (the moving velocity of the rubbingcloth/the moving velocity of the substrate film) was set to 4.

On the resulting alignment substrate was spin-coated the liquid crystalmaterial solution prepared in Example 1. The coated alignment substratewas dried on a hot plate kept at 60° C. for 10 minutes and heated at150° C. in an oven for 2 minutes thereby aligning the liquid crystalmaterial. The sample was placed on an aluminum plate heated at 60° C.,making contact therewith and irradiated with an ultraviolet light of 600mJ/cm² (measured at 365 nm) using a high pressure mercury lamp therebycuring the liquid crystal material.

Since the polyethylene naphthalate film used as a substrate was large inbirefringence and thus not preferable for an optical film, the resultingliquid crystal film on the alignment substrate was transferred via anultraviolet curing type adhesive onto a triacetylcellulose (TAC) film.More specifically, the adhesive with a thickness of 5 μm was coated overthe cured liquid crystal material layer on the polyethylene naphthalatefilm and laminated with a TAC film. After the laminate was subjected toan irradiation of ultraviolet light from the TAC film side so as to curethe adhesive, the polyethylene naphthalate film was released.

As a result of observation of the resulting optical film (PVAlayer/liquid crystal layer/adhesive layer/TAC film) through a polarizingmicroscope, it was confirmed that the film was aligned in a monodomainuniform aligned state having no disclination. As a result of observationof the optical film through a conoscope, it was confirmed that thealignment was a homeotropic alignment having a positive uniaxialrefraction structure. As the result of measurement using KOBRA21ADH, thecombination of the TAC film and the liquid crystal film was found tohave a retardation in the plane direction (Re1) of 0.5 nm and aretardation in the thickness direction (Rth1) of −50 nm. The TAC filmitself had a negative uniaxiality and a retardation in the plane of 0.5nm and a retardation in the thickness of +40 nm. Therefore, it wasassessed that the liquid crystal layer itself had an Re of 0.5 nm and anRth of −90 nm.

EXAMPLE 9

An optical film was prepared in accordance with the procedures ofExample 8 except that the thickness of the homeotropic alignment liquidcrystal film was changed to 1.0 μm. As the result of measurement usingKOBRA21ADH, the combination of the TAC film and the liquid crystal layerwas found to have a retardation in the plane direction (Re1) of 0.5 nmand a retardation in the thickness direction (Rth1) of −125 nm. The TACfilm itself had a negative uniaxiality and a retardation in the plane of0.5 nm and a retardation in the thickness direction of +40 nm.Therefore, it was assessed that the liquid crystal layer itself had anRe1 of 0.5 nm and an Rth1 of −165 nm.

EXAMPLE 10

An optical film was prepared in accordance with the procedures ofExample 8 except that the thickness of the homeotropic alignment liquidcrystal film was changed to 0.9 μm. As the result of measurement usingKOBRA21ADH, the combination of the TAC film and the liquid crystal layerwas found to have a retardation in the plane direction (Re1) of 0.5 nmand a retardation in the thickness direction (Rth1) of −95 nm. The TACfilm itself had a negative uniaxiality and a retardation in the plane of0.5 nm and a retardation in the thickness direction of +40 nm.Therefore, it was assessed that the liquid crystal layer itself had anRe1 of 0.5 nm and an Rth1 of −135 nm.

EXAMPLE 11

The vertical alignment type liquid crystal display device of Example 11will be described with reference to FIGS. 3 and 4.

A transparent electrode 3 formed with an ITO layer with hightransmissivity was formed on a substrate 1, and a counter electrode 4was formed on a substrate 2. Between the transparent electrode 3 and thecounter electrode 3 was sandwiched a liquid crystal layer 5 formed witha liquid crystal material exhibiting a negative dielectric anisotropy.

On the contacting surfaces between the liquid crystal layer 5 and thetransparent electrode 3 and the counter electrode 4 were formed verticalalignment films (not shown), at least one of which had been subjected toan aligning treatment such as rubbing after being coated.

The liquid crystal molecules in the liquid crystal layer 5 had a tiltangle of 1 degree due to the alignment treatment such as rubbing on thealignment film.

Because of the use of the liquid crystal material exhibiting a negativedielectric anisotropy for the liquid crystal layer 5, the liquid crystalmolecules tilted toward the parallel direction upon application of anelectric voltage between the transparent electrode 3 and the counterelectrode 4.

As the liquid crystal material for the liquid crystal layer 5 was used aliquid crystal material having a refractive index anisotropy wherein Ne(refractive index to extraordinary light)=1.561, No (refractive index toordinary light)=1.478, and ΔN(Ne−No)=0.083.

A linear polarizing film 7 (thickness: about 180 μm, SQW-862manufactured by Sumitomo Chemical Co., Ltd.) was arranged above thedisplaying side (upper side of the drawing) of the vertical alignmenttype liquid crystal cell 6. Between the upper linear polarizing film 7and the liquid crystal cell 6 were arranged a third optical anisotropicelement 8 (ARTON manufactured by JSR Corporation), a first opticalanisotropic element (ZEONOR manufactured by ZEON CORPORATION), and thehomeotropic alignment liquid crystal film 10 prepared in Example 8. Alinear polarizing film 11 (thickness: about 180 μm SQW-862 manufacturedby Sumitomo Chemical Co., Ltd.) was arranged below the rear side (lowerside of the drawing) of the vertical alignment type liquid crystal cell6. Between the lower linear polarizing film 11 and the liquid crystalcell 6 were arranged another third optical anisotropic element 12 (ARTONmanufactured by JSR Corporation), another first optical anisotropicelement 13 (ZEONOR manufactured by ZEON CORPORATION), and thehomeotropic alignment liquid crystal film 14 prepared in Example 1.

The first optical anisotropic elements 9, 13 were each formed with anoptical element having an optical axis in the plane and a positiveuniaxial optical anisotropy. The absorption axis orientations of thelinear polarizing films 7, 11 were set to 45 degrees and 135 degrees inthe plane, respectively, as indicated by arrows in FIG. 4. The slow axisorientations of the first optical anisotropic elements 9, 13 were set to90 degrees and 0 degree, respectively, as indicated by arrows in FIG. 4,and they had a retardation in the plane Re2 of 137.5 nm.

The third optical anisotropic elements 8, 12 had each a retardation inthe plane Re4 of substantially zero nm and a retardation in thethickness of 130 nm.

The homeotropic alignment liquid crystal films 10, 14 had each aretardation in the plane Re1 of 0.5 nm and a retardation in thethickness Rth1 of −50 nm.

FIG. 5 shows the contrast ratio from all the directions defined by thetransmissivity ratio of black image 0V and white image 5V “(whiteimage)/(black image)”. The concentric circles indicate same viewingangles and each of the intervals between the circles indicates 20degrees. Therefore, the outermost circle indicates 80 degrees.

EXAMPLE 12

The vertical alignment type liquid crystal display device of Example 12will be described with reference to FIGS. 6 and 7.

The vertical alignment type liquid crystal display device was producedin accordance with the procedures of Example 11 except that the firstoptical anisotropic elements 9, 13 (ZEONOR manufactured by ZEONCORPORATION) used in Example 11 were converted to those having anegative optical anisotropy using the homeotropic alignment liquidcrystal film prepared in Example 9 and the third optical anisotropicelements 8, 12 were excluded.

The absorption axis orientations of the linear polarizing films 7, 11were set to 45 degrees and 135 degrees in the planes, respectively, asindicated by arrows in FIG. 7. The slow axis orientations of the firstoptical anisotropic elements 9, 13 were set to 90 degrees and 0 degree,respectively, as indicated by arrows in FIG. 7, and they had aretardation in the plane Re2 of 137.5 nm wherein the NZ coefficient=2.5.

The homeotropic alignment liquid crystal films 10, 14 had each aretardation in the plane Re1 of 0.5 nm and a retardation in thethickness Rth1 of −125 nm.

FIG. 8 shows the contrast ratio from all the directions defined by thetransmissivity ratio of black image 0V and white image 5V “(whiteimage)/(black image)”. The concentric circles indicate same viewingangles and each of the intervals between the circles indicates 20degrees. Therefore, the outermost circle indicates 80 degrees.

EXAMPLE 13

The vertical alignment type liquid crystal display device of Example 13will be described with reference to FIGS. 9 and 10.

A reflective electrode 15 formed with an Al layer with high reflectivityand a transparent electrode formed with an ITO layer with hightransmissivity were formed on a substrate 1, and a counter electrode 4was formed on a substrate 2. Between the reflective and transparentelectrodes 15, 3 and the counter electrode 4 was sandwiched a liquidcrystal layer 5 formed from a liquid crystal material exhibiting anegative dielectric anisotropy.

On the contacting surfaces between the liquid crystal layer 5 and thereflective and transparent electrodes 15, 3 and the counter electrode 4were formed vertical alignment films (not shown), at least one of whichhad been subjected to a aligning treatment such as rubbing after beingcoated.

The liquid crystal molecules in the liquid crystal layer 5 had a tiltangle of 1 degree due to the alignment treatment such as rubbing on thealignment film.

Because of the use of the liquid crystal material exhibiting a negativedielectric anisotropy for the liquid crystal layer 5, the liquid crystalmolecules tilted toward the parallel direction upon application of anelectric voltage between the reflective and transparent electrodes 15, 3and the counter electrode 4.

As the liquid crystal material for the liquid crystal layer 5 was usedthe same material as that used in Example 10.

A linear polarizing film 7 (thickness: about 180 μm, SQW-862manufactured by Sumitomo Chemical Co., Ltd.) was arranged above thedisplaying side (upper side of the drawing) of the vertical alignmenttype liquid crystal cell 16. Between the upper linear polarizing film 7and the liquid crystal cell 16 were arranged a third optical anisotropicelement 8 (ARTON manufactured by JSR Corporation), a first opticalanisotropic element 9 (ZEONOR manufactured by ZEON CORPORATION), asecond optical anisotropic element 17 (ZEONOR manufactured by ZEONCORPORATION) and the homeotropic alignment liquid crystal film 10prepared in Example 10. A linear polarizing film 11 (thickness: about180 μm, SQW-862 manufactured by Sumitomo Chemical Co., Ltd.) wasarranged below the rear side (lower side of the drawing) of the verticalalignment type liquid crystal cell 16. Between the lower linearpolarizing film 11 and the liquid crystal cell 16 were arranged anotherthird optical anisotropic element 12 (ARTON manufactured by JSRCorporation), another first optical anisotropic element 13 (ZEONORmanufactured by ZEON CORPORATION), another second optical anisotropicelement 18 (ZEONOR manufactured by ZEON CORPORATION) and the homeotropicalignment liquid crystal film 14 prepared in Example 10.

The first optical anisotropic elements 9, 13 and second opticalanisotropic elements 17, 18 were each formed with an optical elementhaving an optical axis in the plane and a positive uniaxial anisotropy.The absorption axis orientations of the linear polarizing films 7, 11are set to 15 degrees and 105 degrees in the planes, respectively, asindicated by arrows in FIG. 10. The slow axis orientations of the firstoptical anisotropic elements 9, 13 were set to 90 degrees and 0 degree,respectively, as indicated by arrows in FIG. 10, and they had aretardation in the plane Re2 of 137.5 nm. The slow axis orientations ofthe second optical anisotropic elements 17, 18 were set to 30 degreesand 120 degrees, respectively, as indicated by arrows in FIG. 10, andthey had a retardation in the plane Re3 of 275 nm.

The third optical anisotropic elements 8, 12 had a retardation in theplane Re4 of substantially zero nm and a retardation in the thicknessRth of 105 nm.

The homeotropic alignment liquid crystal films 10, 14 had each aretardation in the plane Re1 of 0.5 nm and a retardation in thethickness Rth1 of −95 nm.

FIG. 11 shows the contrast ratio from all the directions defined by thetransmissivity ratio of black image 0V and white image 5V “(whiteimage)/(black image)”. The concentric circles indicate same viewingangles and each of the intervals between the circles indicates 20degrees. Therefore, the outermost circle indicates 80 degrees.

COMPARATIVE EXAMPLE 2

The vertical alignment type liquid crystal display device shown in FIG.12 was prepared in accordance with the procedures of Example 11 exceptthat the homeotropic alignment liquid crystal films 10, 14 were notused.

FIG. 13 shows the angle relation in each component.

FIG. 14 shows the contrast ratio from all the directions defined by thetransmissivity ratio of black image 0V and white image 5V “(whiteimage)/(black image)”. The concentric circles indicate same viewingangles and each of the intervals between the circles indicates 20degrees. Therefore, the outermost circle indicates 80 degrees.

From the comparison between the contrast contours in the all directionshown in FIGS. 5 and 8 and those in FIG. 14, it was found that widerviewing characteristics was able to be obtained when using thehomeotropic alignment liquid crystal films.

COMPARATIVE EXAMPLE 3

The transflective vertical alignment type liquid crystal display deviceshown in FIG. 15 was prepared in accordance with the procedures ofExample 13 except that the homeotropic alignment liquid crystal films10, 14 were not used.

FIG. 16 shows the angle relation in each component.

FIG. 17 shows the contrast ratio from all the directions defined by thetransmissivity ratio of black image 0V and white image 5V “(whiteimage)/(black image)”. The concentric circles indicate same viewingangles and each of the intervals between the circles indicates 20degrees. Therefore, the outermost circle indicates 80 degrees.

From the comparison between the contrast contours in the all directionshown in FIG. 11 and those in FIG. 17, it was found that wider viewingcharacteristics was able to be obtained when using the homeotropicalignment liquid crystal films.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

We claim:
 1. A vertical alignment liquid crystal display devicecomprising: a vertical alignment type liquid crystal cell containing apair of substrates each having an electrode, and liquid crystalmolecules to be aligned vertically to the substrate surface when noelectric voltage is applied, arranged between the substrates; two linearpolarizing films arranged above and below the liquid crystal cell; firstoptical anisotropic elements exhibiting a retardation of 1/4 wavelengthin the plane, arranged between both surfaces of the liquid crystal celland the linear polarizing films; and at least one viewing anglecompensator arranged between the linear polarizing films and the firstoptical anisotropic elements, wherein said viewing angle compensatorcomprises a homeotropic alignment liquid crystal film comprising aliquid crystalline substance containing a side chain liquid crystallinecompound having an oxetanyl group, as a constituent, alignedhomeotropically on an alignment substrate while the substance is in aliquid crystal state and fixed in the homeotropic alignment by allowingthe oxetanyl group to react and satisfies the following requirements:[7] 0 nm≦Re1≦20 nm [8] −500 nm≦Rth1≦−30 nm wherein Re1 indicates theretardation value in the plane of the homeotropic alignment liquidcrystal film, Rth1 indicates the retardation value in the thicknessdirection of the homeotropic alignment liquid crystal film, Re1 and Rth1are defined by Rel=(Nxl−Nyl)xd1 [nm] and Rth1 =(Nx1−Nzl)xd1 [nm],respectively wherein dl indicates the thickness of the homeotropicalignment liquid crystal film, Nx1 and Ny 1 indicate the main refractiveindices in the plane of the homeotropic alignment liquid crystal film,Nz1 indicates the main refractive index in the thickness direction ofthe homeotropic alignment liquid crystal film, and Nz1 >Nx1 Ny1.
 2. Thevertical alignment liquid crystal display device according to claim 1,further comprising a second optical anisotropic element having aretardation of ½wavelength in the plane, arranged between the firstoptical anisotropic element and the viewing angle compensator.
 3. Thevertical alignment liquid crystal display device according to claim 2,further comprising at least one third optical anisotropic element havinga negative uniaxial optical anisotropy in the thickness direction,arranged between the first optical anisotropic elements and one or bothsurfaces of the liquid crystal cell.
 4. The vertical alignment liquidcrystal display device according to claim 1, wherein the first opticalanisotropic element has a retardation of 1/4 wavelength in the plane anda negative biaxial optical anisotropy in the thickness direction.
 5. Thevertical alignment liquid crystal display device according to claim 1,wherein one of the substrates of the vertical alignment type liquidcrystal cell has a region with reflectivity and a region withtransmissivity.